Fix Calendar: Uppercase MAILTO calendar addresses become invalid SMTP recipients

CHANGELOG.md

@@ -13,6 +13,7 @@ If you are upgrading from v0.16.x, replace the binary (or run `docker pull`). If
 ## Fixed
 - IMAP: Mailbox object-quota only enforced in JMAP.
 - JMAP: Read-only sharee cannot set `isSubscribed` on a shared mailbox.
+- Calendar: Uppercase `MAILTO` calendar addresses become invalid SMTP recipients.
 
 ## [0.16.13] - 2026-07-12
 

crates/dav/src/calendar/scheduling.rs

@@ -29,7 +29,9 @@ use dav_proto::{
         response::{CalCondition, Href, ScheduleResponse, ScheduleResponseItem},
     },
 };
-use groupware::{DestroyArchive, cache::GroupwareCache, calendar::CalendarEventNotification};
+use groupware::{
+    DestroyArchive, cache::GroupwareCache, calendar::CalendarEventNotification, strip_mailto_scheme,
+};
 use http_proto::HttpResponse;
 use hyper::StatusCode;
 use store::{
@@ -325,9 +327,7 @@ impl CalendarEventNotificationHandler for Server {
                             ICalendarValue::Text(value) | ICalendarValue::Uri(Uri::Location(value)),
                         ),
                     ) => {
-                        if let Some(email) =
-                            sanitize_email(value.strip_prefix("mailto:").unwrap_or(value.as_str()))
-                        {
+                        if let Some(email) = sanitize_email(strip_mailto_scheme(value.as_str())) {
                             attendees.insert(email, entry);
                         }
                     }

crates/groupware/src/calendar/index.rs

@@ -8,9 +8,12 @@ use super::{
     ArchivedCalendar, ArchivedCalendarEvent, ArchivedCalendarPreferences, ArchivedDefaultAlert,
     ArchivedTimezone, Calendar, CalendarEvent, CalendarPreferences, DefaultAlert, Timezone,
 };
-use crate::calendar::{
-    ArchivedCalendarEventNotification, ArchivedChangedBy, ArchivedEventPreferences,
-    CalendarEventNotification, ChangedBy, EventPreferences,
+use crate::{
+    calendar::{
+        ArchivedCalendarEventNotification, ArchivedChangedBy, ArchivedEventPreferences,
+        CalendarEventNotification, ChangedBy, EventPreferences,
+    },
+    strip_mailto_scheme,
 };
 use ahash::AHashSet;
 use calcard::icalendar::{
@@ -463,7 +466,7 @@ impl ArchivedCalendarEvent {
                             _ => None,
                         }))
                     {
-                        let value = value.strip_prefix("mailto:").unwrap_or(value).trim();
+                        let value = strip_mailto_scheme(value);
                         let lang = if is_lang {
                             detector.detect(value, MIN_LANGUAGE_SCORE);
                             Language::Unknown

crates/groupware/src/lib.rs

@@ -149,3 +149,10 @@ impl DavCalendarResource for DavResources {
             .map(|p| p.tz)
     }
 }
+
+pub fn strip_mailto_scheme(value: &str) -> &str {
+    value
+        .split_once(':')
+        .filter(|(scheme, _)| scheme.eq_ignore_ascii_case("mailto"))
+        .map_or(value, |(_, address)| address.trim())
+}

crates/groupware/src/scheduling/mod.rs

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
+use crate::strip_mailto_scheme;
 use ahash::{AHashMap, AHashSet};
 use calcard::{
     common::{IanaString, PartialDateTime},
@@ -238,7 +239,7 @@ impl Attendee<'_> {
 impl Email {
     pub fn new(email: &str, local_addresses: &[String]) -> Option<Self> {
         email.contains('@').then(|| {
-            let email = email.trim().trim_start_matches("mailto:").to_lowercase();
+            let email = strip_mailto_scheme(email.trim()).to_lowercase();
             let is_local = local_addresses.contains(&email);
             Email { email, is_local }
         })

crates/jmap/src/participant_identity/set.rs

@@ -6,7 +6,10 @@
 
 use crate::participant_identity::get::ParticipantIdentityGet;
 use common::Server;
-use groupware::calendar::{ParticipantIdentities, ParticipantIdentity};
+use groupware::{
+    calendar::{ParticipantIdentities, ParticipantIdentity},
+    strip_mailto_scheme,
+};
 use jmap_proto::{
     error::set::{SetError, SetErrorType},
     method::set::{SetRequest, SetResponse},
@@ -226,11 +229,7 @@ fn validate_identity_value(
             }
             (ParticipantIdentityProperty::CalendarAddress, Value::Str(value)) => {
                 if identity.calendar_address != value {
-                    let email = if let Some(email) = value.strip_prefix("mailto:") {
-                        sanitize_email(email)
-                    } else {
-                        sanitize_email(&value)
-                    };
+                    let email = sanitize_email(strip_mailto_scheme(&value));
 
                     if let Some(email) = email {
                         if allowed_emails.iter().any(|e| e == &email) {

crates/jmap/src/principal/availability.rs

@@ -21,6 +21,7 @@ use common::{
 use groupware::{
     cache::GroupwareCache,
     calendar::{CALENDAR_SUBSCRIBED, CalendarEvent},
+    strip_mailto_scheme,
 };
 use jmap_proto::{
     method::availability::{
@@ -258,9 +259,7 @@ impl PrincipalGetAvailability for Server {
                                 if include_in_availability == IncludeInAvailability::Attending =>
                             {
                                 if let Some(attendee) = value.as_text().and_then(|attendee| {
-                                    sanitize_email(
-                                        attendee.strip_prefix("mailto:").unwrap_or(attendee),
-                                    )
+                                    sanitize_email(strip_mailto_scheme(attendee))
                                 }) {
                                     // Condition: the Principal is a participant of the event, and has a "participationStatus" of "accepted" or "tentative".
                                     if principal_account.addresses().contains(&attendee) {

crates/services/src/task_manager/alarm.rs

@@ -17,7 +17,10 @@ use common::{
     ipc::{CalendarAlert, PushNotification},
     network::{ServerInstance, stream::NullIo},
 };
-use groupware::calendar::{ArchivedCalendarEvent, CalendarEvent};
+use groupware::{
+    calendar::{ArchivedCalendarEvent, CalendarEvent},
+    strip_mailto_scheme,
+};
 use mail_builder::{
     MessageBuilder,
     headers::{HeaderType, content_type::ContentType},
@@ -478,7 +481,7 @@ async fn build_template(
                     .values
                     .first()
                     .and_then(|v| v.as_text())
-                    .map(|v| v.strip_prefix("mailto:").unwrap_or(v))
+                    .map(strip_mailto_scheme)
                     .and_then(sanitize_email);
             }
             _ => {}
@@ -501,7 +504,7 @@ async fn build_template(
                     .values
                     .first()
                     .and_then(|v| v.as_text())
-                    .map(|v| v.strip_prefix("mailto:").unwrap_or(v));
+                    .map(strip_mailto_scheme);
                 let name = entry.params.iter().find_map(|param| {
                     if let ArchivedICalendarParameterName::Cn = param.name {
                         param.value.as_text()