Add email verification for Sends

Allow Sends to be restricted to a list of email addresses. Recipients
request a one-time code by email through the `send_access` grant and
exchange it for an access token, matching the upstream flow.

- Store `auth_type` and `emails` on sends, with an additive migration
- One-time codes: single use, constant-time compared, invalidated after
  5 wrong attempts, 60s resend cooldown, 5 minute validity
- Unlisted emails get the same response as listed ones and no email is
  sent, so recipients can't be enumerated
- Access is gated on the stored auth type and fails closed when a Send
  doesn't hold the emails or password its auth type requires
- Shared create/update handling of authType; it is inferred when
  missing, like upstream, for clients that don't send it

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

migrations/mysql/2026-10-16-120000_add_send_email_verification/down.sql

@@ -0,0 +1,3 @@
+DROP TABLE send_access_otps;
+ALTER TABLE sends DROP COLUMN emails;
+ALTER TABLE sends DROP COLUMN auth_type;

migrations/mysql/2026-10-16-120000_add_send_email_verification/up.sql

@@ -0,0 +1,15 @@
+ALTER TABLE sends ADD COLUMN auth_type INTEGER NOT NULL DEFAULT 2;
+UPDATE sends SET auth_type = 1 WHERE password_hash IS NOT NULL;
+ALTER TABLE sends ADD COLUMN emails TEXT;
+
+CREATE TABLE send_access_otps (
+  send_uuid       CHAR(36)     NOT NULL,
+  email           VARCHAR(255) NOT NULL,
+  code            TEXT         NOT NULL,
+  attempts        INTEGER      NOT NULL DEFAULT 0,
+  creation_date   DATETIME     NOT NULL,
+  expiration_date DATETIME     NOT NULL,
+
+  PRIMARY KEY (send_uuid, email),
+  FOREIGN KEY (send_uuid) REFERENCES sends (uuid) ON DELETE CASCADE
+);

migrations/postgresql/2026-10-16-120000_add_send_email_verification/down.sql

@@ -0,0 +1,3 @@
+DROP TABLE send_access_otps;
+ALTER TABLE sends DROP COLUMN emails;
+ALTER TABLE sends DROP COLUMN auth_type;

migrations/postgresql/2026-10-16-120000_add_send_email_verification/up.sql

@@ -0,0 +1,15 @@
+ALTER TABLE sends ADD COLUMN auth_type INTEGER NOT NULL DEFAULT 2;
+UPDATE sends SET auth_type = 1 WHERE password_hash IS NOT NULL;
+ALTER TABLE sends ADD COLUMN emails TEXT;
+
+CREATE TABLE send_access_otps (
+  send_uuid       CHAR(36)     NOT NULL,
+  email           VARCHAR(255) NOT NULL,
+  code            TEXT         NOT NULL,
+  attempts        INTEGER      NOT NULL DEFAULT 0,
+  creation_date   TIMESTAMP    NOT NULL,
+  expiration_date TIMESTAMP    NOT NULL,
+
+  PRIMARY KEY (send_uuid, email),
+  FOREIGN KEY (send_uuid) REFERENCES sends (uuid) ON DELETE CASCADE
+);

migrations/sqlite/2026-10-16-120000_add_send_email_verification/down.sql

@@ -0,0 +1,3 @@
+DROP TABLE send_access_otps;
+ALTER TABLE sends DROP COLUMN emails;
+ALTER TABLE sends DROP COLUMN auth_type;

migrations/sqlite/2026-10-16-120000_add_send_email_verification/up.sql

@@ -0,0 +1,15 @@
+ALTER TABLE sends ADD COLUMN auth_type INTEGER NOT NULL DEFAULT 2;
+UPDATE sends SET auth_type = 1 WHERE password_hash IS NOT NULL;
+ALTER TABLE sends ADD COLUMN emails TEXT;
+
+CREATE TABLE send_access_otps (
+  send_uuid       TEXT     NOT NULL,
+  email           TEXT     NOT NULL,
+  code            TEXT     NOT NULL,
+  attempts        INTEGER  NOT NULL DEFAULT 0,
+  creation_date   DATETIME NOT NULL,
+  expiration_date DATETIME NOT NULL,
+
+  PRIMARY KEY (send_uuid, email),
+  FOREIGN KEY (send_uuid) REFERENCES sends (uuid) ON DELETE CASCADE
+);

src/api/core/sends.rs

@@ -1,7 +1,7 @@
 use std::{path::Path, sync::LazyLock, time::Duration};
 
 use chrono::{DateTime, TimeDelta, Utc};
-use num_traits::ToPrimitive;
+use num_traits::{FromPrimitive, ToPrimitive};
 use rocket::{
     form::Form,
     fs::{NamedFile, TempFile},
@@ -16,7 +16,7 @@ use crate::{
     config::PathType,
     db::{
         DbConn, DbPool,
-        models::{Device, OrgPolicy, OrgPolicyType, Send, SendFileId, SendId, SendType, UserId},
+        models::{Device, OrgPolicy, OrgPolicyType, Send, SendAuthType, SendFileId, SendId, SendType, UserId},
     },
     util::{NumberOrString, save_temp_file},
 };
@@ -77,6 +77,7 @@ pub struct SendData {
     deletion_date: DateTime<Utc>,
     disabled: bool,
     hide_email: Option<bool>,
+    auth_type: Option<i32>,
     emails: Option<String>,
 
     // Data field
@@ -148,10 +149,6 @@ fn create_send(data: SendData, user_id: UserId) -> ApiResult<Send> {
         );
     }
 
-    if data.emails.is_some() {
-        err!("Sends with email verification is not supported");
-    }
-
     let mut send = Send::new(data.r#type, data.name, data_str, data.key, data.deletion_date.naive_utc());
     send.user_uuid = Some(user_id);
     send.notes = data.notes;
@@ -164,11 +161,85 @@ fn create_send(data: SendData, user_id: UserId) -> ApiResult<Send> {
     send.hide_email = data.hide_email;
     send.atype = data.r#type;
 
-    send.set_password(data.password.as_deref());
+    apply_send_auth(&mut send, data.auth_type, data.emails.as_deref(), data.password)?;
+    enforce_mail_enabled_for_email_auth(&send)?;
 
     Ok(send)
 }
 
+/// Splits a comma separated list of emails, trimming and lowercasing each entry and dropping empty ones.
+/// Returns `None` when no address is left.
+fn normalize_emails(emails: Option<&str>) -> Option<String> {
+    let emails: Vec<String> = emails?.split(',').map(|e| e.trim().to_lowercase()).filter(|e| !e.is_empty()).collect();
+    (!emails.is_empty()).then(|| emails.join(","))
+}
+
+/// Applies the requested access control to a Send, used for both creation and updates.
+///
+/// When `authType` is missing (older clients) it is inferred from the other fields, like upstream does.
+/// The stored `auth_type` is always derived from the resulting state, so a Send never claims a
+/// protection it doesn't actually enforce.
+///
+/// Upstream: https://github.com/bitwarden/server/blob/main/src/Api/Tools/Models/Request/SendRequestModel.cs
+fn apply_send_auth(
+    send: &mut Send,
+    auth_type: Option<i32>,
+    emails: Option<&str>,
+    password: Option<String>,
+) -> EmptyResult {
+    let auth_type = match auth_type.map(SendAuthType::from_i32) {
+        Some(None) => err!("Invalid authType"),
+        Some(t) => t,
+        None => None,
+    };
+    let emails = normalize_emails(emails);
+    let password = password.filter(|p| !p.is_empty());
+
+    match auth_type {
+        Some(SendAuthType::Email) => {
+            let Some(emails) = emails else {
+                err!("Email verification requires at least one email address")
+            };
+            send.emails = Some(emails);
+            send.set_password(None);
+        }
+        Some(SendAuthType::Password) => {
+            send.emails = None;
+            // Editing a password protected Send doesn't resend the password, keep the existing one
+            if let Some(password) = password {
+                send.set_password(Some(&password));
+            } else if send.password_hash.is_none() {
+                err!("A password is required")
+            }
+        }
+        Some(SendAuthType::None) => {
+            send.emails = None;
+            send.set_password(None);
+        }
+        // Unlike upstream, an email protected Send is kept as is when no emails are provided, clients
+        // without `authType` don't know about emails so they can't have intentionally removed them.
+        None => {
+            if emails.is_some() {
+                send.emails = emails;
+                send.set_password(None);
+            } else if let Some(password) = password {
+                send.emails = None;
+                send.set_password(Some(&password));
+            }
+        }
+    }
+
+    send.auth_type = send.effective_auth_type() as i32;
+    Ok(())
+}
+
+fn enforce_mail_enabled_for_email_auth(send: &Send) -> EmptyResult {
+    if send.emails.is_some() && !CONFIG.mail_enabled() {
+        err!("Email verification for Sends requires email to be enabled on this server")
+    }
+    Ok(())
+}
+
 #[get("/sends")]
 async fn get_sends(headers: Headers, conn: DbConn) -> Json<Value> {
     let sends = Send::find_by_user(&headers.user.uuid, &conn);
@@ -473,10 +544,6 @@ async fn put_send(send_id: SendId, data: Json<SendData>, headers: Headers, conn:
         err!("Send not found", "Send send_id is invalid or does not belong to user")
     };
 
-    if data.emails.is_some() {
-        err!("Sends with email verification is not supported");
-    }
-
     update_send_from_data(&mut send, data, &headers, &conn, &nt, UpdateType::SyncSendUpdate).await?;
 
     Ok(Json(send.to_json()))
@@ -528,10 +595,8 @@ async fn update_send_from_data(
     send.hide_email = data.hide_email;
     send.disabled = data.disabled;
 
-    // Only change the value if it's present
-    if let Some(password) = data.password {
-        send.set_password(Some(&password));
-    }
+    apply_send_auth(send, data.auth_type, data.emails.as_deref(), data.password)?;
+    enforce_mail_enabled_for_email_auth(send)?;
 
     send.save(conn).await?;
     if ut != UpdateType::None {
@@ -568,6 +633,7 @@ async fn put_remove_password(send_id: SendId, headers: Headers, conn: DbConn, nt
     };
 
     send.set_password(None);
+    send.auth_type = send.effective_auth_type() as i32;
     send.save(&conn).await?;
     nt.send_send_update(
         UpdateType::SyncSendUpdate,
@@ -580,3 +646,94 @@ async fn put_remove_password(send_id: SendId, headers: Headers, conn: DbConn, nt
 
     Ok(Json(send.to_json()))
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn new_send() -> Send {
+        Send::new(
+            SendType::Text as i32,
+            String::from("name"),
+            String::from("{}"),
+            String::from("key"),
+            Utc::now().naive_utc(),
+        )
+    }
+
+    const EMAIL: i32 = SendAuthType::Email as i32;
+    const PASSWORD: i32 = SendAuthType::Password as i32;
+    const NONE: i32 = SendAuthType::None as i32;
+
+    #[test]
+    fn test_normalize_emails() {
+        assert_eq!(normalize_emails(Some(" A@x.com, ,b@X.com ,")).as_deref(), Some("a@x.com,b@x.com"));
+        assert_eq!(normalize_emails(Some(" , ")), None);
+        assert_eq!(normalize_emails(Some("")), None);
+        assert_eq!(normalize_emails(None), None);
+    }
+
+    #[test]
+    fn test_email_auth_requires_an_email() {
+        let mut send = new_send();
+        assert!(apply_send_auth(&mut send, Some(EMAIL), Some(" , "), None).is_err());
+        assert!(apply_send_auth(&mut send, Some(EMAIL), None, None).is_err());
+    }
+
+    #[test]
+    fn test_email_auth_clears_password() {
+        let mut send = new_send();
+        apply_send_auth(&mut send, Some(PASSWORD), None, Some(String::from("secret"))).unwrap();
+        apply_send_auth(&mut send, Some(EMAIL), Some("A@x.com"), Some(String::from("secret"))).unwrap();
+        assert_eq!(send.auth_type, EMAIL);
+        assert_eq!(send.emails.as_deref(), Some("a@x.com"));
+        assert!(send.password_hash.is_none());
+    }
+
+    #[test]
+    fn test_password_auth() {
+        let mut send = new_send();
+        assert!(apply_send_auth(&mut send, Some(PASSWORD), None, None).is_err());
+
+        apply_send_auth(&mut send, Some(PASSWORD), Some("a@x.com"), Some(String::from("secret"))).unwrap();
+        assert_eq!(send.auth_type, PASSWORD);
+        assert!(send.emails.is_none());
+
+        // Edits don't resend the password, the existing one is kept
+        apply_send_auth(&mut send, Some(PASSWORD), None, None).unwrap();
+        assert_eq!(send.auth_type, PASSWORD);
+        assert!(send.check_password("secret"));
+    }
+
+    #[test]
+    fn test_none_auth_clears_everything() {
+        let mut send = new_send();
+        apply_send_auth(&mut send, Some(EMAIL), Some("a@x.com"), None).unwrap();
+        apply_send_auth(&mut send, Some(NONE), Some("a@x.com"), Some(String::from("secret"))).unwrap();
+        assert_eq!(send.auth_type, NONE);
+        assert!(send.emails.is_none());
+        assert!(send.password_hash.is_none());
+    }
+
+    #[test]
+    fn test_missing_auth_type_is_inferred() {
+        let mut send = new_send();
+        apply_send_auth(&mut send, None, None, Some(String::from("secret"))).unwrap();
+        assert_eq!(send.auth_type, PASSWORD);
+
+        apply_send_auth(&mut send, None, Some("a@x.com"), None).unwrap();
+        assert_eq!(send.auth_type, EMAIL);
+        assert!(send.password_hash.is_none());
+
+        // Clients without authType don't know about emails, an email protected Send stays protected
+        apply_send_auth(&mut send, None, None, None).unwrap();
+        assert_eq!(send.auth_type, EMAIL);
+        assert_eq!(send.emails.as_deref(), Some("a@x.com"));
+    }
+
+    #[test]
+    fn test_invalid_auth_type() {
+        let mut send = new_send();
+        assert!(apply_send_auth(&mut send, Some(42), None, None).is_err());
+    }
+}

src/api/identity.rs

@@ -105,6 +105,8 @@ async fn login(data: Form<ConnectData>, client_header: ClientHeaders, conn: DbCo
             let tokens = auth::SendTokens::generate_tokens(
                 data.send_id.as_ref().unwrap(),
                 data.password_hash_b64,
+                data.email,
+                data.otp,
                 &client_header.ip,
                 &conn,
             )
@@ -1165,6 +1167,8 @@ struct ConnectData {
     // Needed for send access
     send_id: Option<SendId>,
     password_hash_b64: Option<String>,
+    email: Option<String>,
+    otp: Option<String>,
 }
 fn check_is_some<T>(value: Option<&T>, msg: &str) -> EmptyResult {
     if value.is_none() {

src/auth/send.rs

@@ -1,16 +1,20 @@
 use chrono::{TimeDelta, Utc};
+use num_traits::FromPrimitive;
 
 use rocket::request::{FromRequest, Outcome, Request};
 
 use crate::{
+    CONFIG,
     api::ApiResult,
     auth,
     auth::{BasicJwtClaims, ClientIp},
+    crypto,
     db::{
         DbConn,
-        models::{Send, SendId},
+        models::{Send, SendAccessOtp, SendAuthType, SendId},
     },
     error::{Error, ErrorKind},
+    mail,
 };
 
 fn generate_send_access_claims(send_id: &SendId) -> BasicJwtClaims {
@@ -45,7 +49,7 @@ impl SendTokens {
         })
     }
 
-    fn expected_error(msg: &str, error_type: &str) -> ApiResult<SendTokens> {
+    fn expected_error<T>(msg: &str, error_type: &str) -> ApiResult<T> {
         let err = json!({
             "kind": "expected_server",
             "error": "invalid_request",
@@ -55,7 +59,7 @@ impl SendTokens {
         Err(Error::new_msg(msg).with_kind(ErrorKind::Json(err)).silent())
     }
 
-    fn invalid_error(msg: &str, error_type: &str, silent: bool) -> ApiResult<SendTokens> {
+    fn invalid_error<T>(msg: &str, error_type: &str, silent: bool) -> ApiResult<T> {
         let err = json!({
             "kind": "expected_server",
             "error": "invalid_grant",
@@ -68,6 +72,8 @@ impl SendTokens {
     pub async fn generate_tokens(
         access_id: &str,
         password: Option<String>,
+        email: Option<String>,
+        otp: Option<String>,
         ip: &ClientIp,
         conn: &DbConn,
     ) -> ApiResult<SendTokens> {
@@ -89,8 +95,10 @@ impl SendTokens {
             return Self::invalid_error(&format!("Send {send_id}, not accessible"), "send_id_invalid", true);
         }
 
-        if send.password_hash.is_some() {
-            match password {
+        // Rely on the stored auth type and fail closed if the Send doesn't hold what it requires
+        match SendAuthType::from_i32(send.auth_type) {
+            Some(SendAuthType::Email) => Self::verify_email_otp(&send, email, otp, conn).await?,
+            Some(SendAuthType::Password) => match password {
                 Some(ref p) if send.check_password(p) => { /* Nothing to do here */ }
                 Some(_) => {
                     return Self::invalid_error(
@@ -100,6 +108,14 @@ impl SendTokens {
                     );
                 }
                 None => return Self::expected_error("Password required", "password_hash_b64_required"),
+            },
+            Some(SendAuthType::None) if send.password_hash.is_none() && send.emails.is_none() => {}
+            _ => {
+                return Self::invalid_error(
+                    &format!("Send {send_id}, inconsistent access settings"),
+                    "send_id_invalid",
+                    false,
+                );
             }
         }
 
@@ -109,6 +125,65 @@ impl SendTokens {
     }
 }
 
+impl SendTokens {
+    /// Email verification: the first request (without `otp`) emails a code to the recipient, the
+    /// second one exchanges it for an access token.
+    ///
+    /// Unlisted emails get the same response as listed ones and no email is sent, so the list of
+    /// recipients can't be enumerated.
+    ///
+    /// Upstream: https://github.com/bitwarden/server/blob/main/src/Identity/IdentityServer/RequestValidators/SendAccess/SendEmailOtpRequestValidator.cs
+    async fn verify_email_otp(send: &Send, email: Option<String>, otp: Option<String>, conn: &DbConn) -> ApiResult<()> {
+        let Some(allowed_emails) = send.emails.as_deref() else {
+            return Self::invalid_error(&format!("Send {}, no emails to verify", send.uuid), "send_id_invalid", false);
+        };
+        if !CONFIG.mail_enabled() {
+            return Self::invalid_error(
+                &format!("Send {}, email verification without mail enabled", send.uuid),
+                "send_id_invalid",
+                false,
+            );
+        }
+
+        let Some(email) = email.map(|e| e.trim().to_lowercase()).filter(|e| !e.is_empty()) else {
+            return Self::expected_error("Email required", "email_required");
+        };
+        if !allowed_emails.split(',').any(|e| e == email) {
+            return Self::expected_error("Email and OTP required", "email_and_otp_required");
+        }
+
+        let stored = SendAccessOtp::find(&send.uuid, &email, conn).await;
+        let Some(code) = otp.map(|o| o.trim().to_owned()).filter(|o| !o.is_empty()) else {
+            if stored.as_ref().is_none_or(SendAccessOtp::can_resend) {
+                let code = crypto::generate_email_token(CONFIG.email_token_size());
+                let new_otp = SendAccessOtp::new(send.uuid.clone(), email.clone(), code.clone());
+                new_otp.save(conn).await?;
+                if let Err(e) = mail::send_send_access_otp(&email, &code).await {
+                    new_otp.delete(conn).await.ok();
+                    return Err(e);
+                }
+            }
+            return Self::expected_error("Email and OTP required", "email_and_otp_required");
+        };
+
+        let Some(stored) = stored else {
+            return Self::expected_error("Email and OTP required", "email_and_otp_required");
+        };
+        if stored.is_expired() || stored.attempts >= SendAccessOtp::MAX_ATTEMPTS {
+            stored.delete(conn).await?;
+            return Self::expected_error("Email and OTP required", "email_and_otp_required");
+        }
+        if !crypto::ct_eq(&code, &stored.code) {
+            stored.increment_attempts(conn).await?;
+            return Self::expected_error("Email and OTP required", "email_and_otp_required");
+        }
+
+        // Codes are single use
+        stored.delete(conn).await?;
+        Ok(())
+    }
+}
+
 pub struct SendHeaders {
     pub send_id: SendId,
 }

src/config.rs

@@ -1736,6 +1736,7 @@ where
     reg!("email/invite_confirmed", ".html");
     reg!("email/new_device_logged_in", ".html");
     reg!("email/protected_action", ".html");
+    reg!("email/send_access_otp", ".html");
     reg!("email/pw_hint_none", ".html");
     reg!("email/pw_hint_some", ".html");
     reg!("email/recover_twofactor", ".html");

src/db/models/mod.rs

@@ -34,7 +34,7 @@ pub use self::organization::{
     Membership, MembershipId, MembershipStatus, MembershipType, OrgApiKeyId, Organization, OrganizationApiKey,
     OrganizationId,
 };
-pub use self::send::{Send, SendFileId, SendId, SendType};
+pub use self::send::{Send, SendAccessOtp, SendAuthType, SendFileId, SendId, SendType};
 pub use self::sso_auth::{OIDCAuthenticatedUser, OIDCCodeResponseError, SsoAuth};
 pub use self::two_factor::{TwoFactor, TwoFactorType};
 pub use self::two_factor_duo_context::TwoFactorDuoContext;

src/db/models/send.rs

@@ -1,6 +1,6 @@
 use std::path::Path;
 
-use chrono::{NaiveDateTime, Utc};
+use chrono::{NaiveDateTime, TimeDelta, Utc};
 use data_encoding::BASE64URL_NOPAD;
 use derive_more::{AsRef, Deref, Display, From};
 use diesel::prelude::*;
@@ -12,7 +12,10 @@ use crate::{
     CONFIG,
     api::EmptyResult,
     config::PathType,
-    db::{DbConn, schema::sends},
+    db::{
+        DbConn,
+        schema::{send_access_otps, sends},
+    },
     error::MapResult,
     util::{LowerCase, NumberOrString, format_date},
 };
@@ -49,6 +52,8 @@ pub struct Send {
 
     pub disabled: bool,
     pub hide_email: Option<bool>,
+    pub auth_type: i32,
+    pub emails: Option<String>,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, num_derive::FromPrimitive)]
@@ -57,10 +62,10 @@ pub enum SendType {
     File = 1,
 }
 
-enum SendAuthType {
-    #[allow(dead_code)]
+#[derive(Copy, Clone, PartialEq, Eq, num_derive::FromPrimitive)]
+pub enum SendAuthType {
     // Send requires email OTP verification
-    Email = 0, // Not yet supported by Vaultwarden
+    Email = 0,
     // Send requires a password
     Password = 1,
     // Send requires no auth
@@ -96,6 +101,8 @@ impl Send {
 
             disabled: false,
             hide_email: None,
+            auth_type: SendAuthType::None as i32,
+            emails: None,
         }
     }
 
@@ -115,6 +122,17 @@ impl Send {
         }
     }
 
+    /// The protection actually enforced, given the stored emails and password.
+    pub fn effective_auth_type(&self) -> SendAuthType {
+        if self.emails.is_some() {
+            SendAuthType::Email
+        } else if self.password_hash.is_some() {
+            SendAuthType::Password
+        } else {
+            SendAuthType::None
+        }
+    }
+
     pub fn check_password(&self, password: &str) -> bool {
         match (&self.password_hash, &self.password_salt, self.password_iter) {
             (Some(hash), Some(salt), Some(iter)) => {
@@ -166,7 +184,8 @@ impl Send {
             "maxAccessCount": self.max_access_count,
             "accessCount": self.access_count,
             "password": self.password_hash.as_deref().map(|h| BASE64URL_NOPAD.encode(h)),
-            "authType": if self.password_hash.is_some() { SendAuthType::Password as i32 } else { SendAuthType::None as i32 },
+            "authType": self.auth_type,
+            "emails": self.emails,
             "disabled": self.disabled,
             "hideEmail": self.hide_email.unwrap_or(false),
 
@@ -282,17 +301,20 @@ impl Send {
             operator.delete_with(&self.uuid).recursive(true).await.ok();
         }
 
+        SendAccessOtp::delete_all_by_send(&self.uuid, conn).await?;
+
         conn.run(move |conn| {
             diesel::delete(sends::table.filter(sends::uuid.eq(&self.uuid))).execute(conn).map_res("Error deleting send")
         })
         .await
     }
 
-    /// Purge all sends that are past their deletion date.
+    /// Purge all sends that are past their deletion date, and expired access codes.
     pub async fn purge(conn: &DbConn) {
         for send in Self::find_by_past_deletion_date(conn).await {
             send.delete(conn).await.ok();
         }
+        SendAccessOtp::delete_expired(conn).await.ok();
     }
 
     pub async fn update_users_revision(&self, conn: &DbConn) -> Vec<UserId> {
@@ -361,6 +383,124 @@ impl Send {
     }
 }
 
+/// A one-time code emailed to a recipient of an email verified Send.
+#[derive(Identifiable, Queryable, Insertable, AsChangeset)]
+#[diesel(table_name = send_access_otps)]
+#[diesel(primary_key(send_uuid, email))]
+pub struct SendAccessOtp {
+    pub send_uuid: SendId,
+    pub email: String,
+    pub code: String,
+    pub attempts: i32,
+    pub creation_date: NaiveDateTime,
+    pub expiration_date: NaiveDateTime,
+}
+
+impl SendAccessOtp {
+    /// How long a code stays valid.
+    const VALIDITY_MINUTES: i64 = 5;
+    /// Wrong guesses allowed before a code is discarded.
+    pub const MAX_ATTEMPTS: i32 = 5;
+    /// Minimum time before a new code can be requested, so the endpoint can't be used to spam a
+    /// recipient or keep invalidating the code they are about to type.
+    const RESEND_COOLDOWN_SECONDS: i64 = 60;
+
+    pub fn new(send_uuid: SendId, email: String, code: String) -> Self {
+        let now = Utc::now().naive_utc();
+        Self {
+            send_uuid,
+            email,
+            code,
+            attempts: 0,
+            creation_date: now,
+            expiration_date: now + TimeDelta::minutes(Self::VALIDITY_MINUTES),
+        }
+    }
+
+    pub fn is_expired(&self) -> bool {
+        Utc::now().naive_utc() >= self.expiration_date
+    }
+
+    pub fn can_resend(&self) -> bool {
+        self.is_expired()
+            || Utc::now().naive_utc() >= self.creation_date + TimeDelta::seconds(Self::RESEND_COOLDOWN_SECONDS)
+    }
+
+    /// Stores the code, replacing any previous one for the same Send and email.
+    pub async fn save(&self, conn: &DbConn) -> EmptyResult {
+        conn.run(move |conn| {
+            conn.transaction(|conn| {
+                diesel::delete(
+                    send_access_otps::table
+                        .filter(send_access_otps::send_uuid.eq(&self.send_uuid))
+                        .filter(send_access_otps::email.eq(&self.email)),
+                )
+                .execute(conn)?;
+                diesel::insert_into(send_access_otps::table).values(self).execute(conn)
+            })
+            .map_res("Error saving send access otp")
+        })
+        .await
+    }
+
+    pub async fn increment_attempts(&self, conn: &DbConn) -> EmptyResult {
+        conn.run(move |conn| {
+            diesel::update(
+                send_access_otps::table
+                    .filter(send_access_otps::send_uuid.eq(&self.send_uuid))
+                    .filter(send_access_otps::email.eq(&self.email)),
+            )
+            .set(send_access_otps::attempts.eq(send_access_otps::attempts + 1))
+            .execute(conn)
+            .map_res("Error updating send access otp")
+        })
+        .await
+    }
+
+    pub async fn delete(&self, conn: &DbConn) -> EmptyResult {
+        conn.run(move |conn| {
+            diesel::delete(
+                send_access_otps::table
+                    .filter(send_access_otps::send_uuid.eq(&self.send_uuid))
+                    .filter(send_access_otps::email.eq(&self.email)),
+            )
+            .execute(conn)
+            .map_res("Error deleting send access otp")
+        })
+        .await
+    }
+
+    pub async fn delete_all_by_send(send_uuid: &SendId, conn: &DbConn) -> EmptyResult {
+        conn.run(move |conn| {
+            diesel::delete(send_access_otps::table.filter(send_access_otps::send_uuid.eq(send_uuid)))
+                .execute(conn)
+                .map_res("Error deleting send access otps")
+        })
+        .await
+    }
+
+    pub async fn delete_expired(conn: &DbConn) -> EmptyResult {
+        let now = Utc::now().naive_utc();
+        conn.run(move |conn| {
+            diesel::delete(send_access_otps::table.filter(send_access_otps::expiration_date.le(now)))
+                .execute(conn)
+                .map_res("Error deleting expired send access otps")
+        })
+        .await
+    }
+
+    pub async fn find(send_uuid: &SendId, email: &str, conn: &DbConn) -> Option<Self> {
+        conn.run(move |conn| {
+            send_access_otps::table
+                .filter(send_access_otps::send_uuid.eq(send_uuid))
+                .filter(send_access_otps::email.eq(email))
+                .first::<Self>(conn)
+                .ok()
+        })
+        .await
+    }
+}
+
 #[derive(
     Clone,
     Debug,

src/db/schema.rs

@@ -151,6 +151,19 @@ table! {
         deletion_date -> Timestamp,
         disabled -> Bool,
         hide_email -> Nullable<Bool>,
+        auth_type -> Integer,
+        emails -> Nullable<Text>,
+    }
+}
+
+table! {
+    send_access_otps (send_uuid, email) {
+        send_uuid -> Text,
+        email -> Text,
+        code -> Text,
+        attempts -> Integer,
+        creation_date -> Timestamp,
+        expiration_date -> Timestamp,
     }
 }
 
@@ -368,6 +381,7 @@ joinable!(folders_ciphers -> folders (folder_uuid));
 joinable!(org_policies -> organizations (org_uuid));
 joinable!(sends -> organizations (organization_uuid));
 joinable!(sends -> users (user_uuid));
+joinable!(send_access_otps -> sends (send_uuid));
 joinable!(twofactor -> users (user_uuid));
 joinable!(users_collections -> collections (collection_uuid));
 joinable!(users_collections -> users (user_uuid));
@@ -398,6 +412,7 @@ allow_tables_to_appear_in_same_query!(
     org_policies,
     organizations,
     sends,
+    send_access_otps,
     sso_users,
     twofactor,
     users,

src/mail.rs

@@ -671,6 +671,19 @@ pub async fn send_admin_account_recovery(
     send_email(address, &subject, body_html, body_text).await
 }
 
+pub async fn send_send_access_otp(address: &str, token: &str) -> EmptyResult {
+    let (subject, body_html, body_text) = get_text(
+        "email/send_access_otp",
+        json!({
+            "url": CONFIG.domain(),
+            "img_src": CONFIG._smtp_img_src(),
+            "token": token,
+        }),
+    )?;
+
+    send_email(address, &subject, body_html, body_text).await
+}
+
 pub async fn send_protected_action_token(address: &str, token: &str) -> EmptyResult {
     let (subject, body_html, body_text) = get_text(
         "email/protected_action",

src/static/templates/email/send_access_otp.hbs

@@ -0,0 +1,6 @@
+Your Vaultwarden Send Verification Code
+<!---------------->
+Your email verification code is: {{token}}
+
+Use this code to view the Send that was shared with you. It expires in 5 minutes.
+{{> email/email_footer_text }}

src/static/templates/email/send_access_otp.html.hbs

@@ -0,0 +1,16 @@
+Your Vaultwarden Send Verification Code
+<!---------------->
+{{> email/email_header }}
+<table width="100%" cellpadding="0" cellspacing="0" style="margin: 0; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; box-sizing: border-box; font-size: 16px; color: #333; line-height: 25px; -webkit-font-smoothing: antialiased; -webkit-text-size-adjust: none;">
+    <tr style="margin: 0; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; box-sizing: border-box; font-size: 16px; color: #333; line-height: 25px; -webkit-font-smoothing: antialiased; -webkit-text-size-adjust: none;">
+        <td class="content-block" style="font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; box-sizing: border-box; font-size: 16px; color: #333; line-height: 25px; margin: 0; -webkit-font-smoothing: antialiased; padding: 0 0 10px; -webkit-text-size-adjust: none;" valign="top">
+            Your email verification code is: <b>{{token}}</b>
+        </td>
+    </tr>
+    <tr style="margin: 0; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; box-sizing: border-box; font-size: 16px; color: #333; line-height: 25px; -webkit-font-smoothing: antialiased; -webkit-text-size-adjust: none;">
+        <td class="content-block" style="font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; box-sizing: border-box; font-size: 16px; color: #333; line-height: 25px; margin: 0; -webkit-font-smoothing: antialiased; padding: 0 0 10px; -webkit-text-size-adjust: none;" valign="top">
+            Use this code to view the Send that was shared with you. It expires in 5 minutes.
+        </td>
+    </tr>
+</table>
+{{> email/email_footer }}