From b17da02d3ee613c18eae586dff352bada2e1de8f Mon Sep 17 00:00:00 2001
From: Maurus Decimus <11444311+mdecimus@users.noreply.github.com>
Date: Sun, 12 Jul 2026 14:58:31 +0200
Subject: [PATCH] Fix JMAP: Return RFC-3339-conformant UTCDate literals in
 capabilities: min `0001-01-01T00:00:00Z`, max `9999-12-31T23:59:59Z`

---
 CHANGELOG.md                                  |  1 +
 .../src/config/mailstore/capabilities.rs      | 25 ++++++++++++++++---
 tests/src/jmap/principal/get.rs               |  2 +-
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 97610f6b..58195c74 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ If you are upgrading from v0.16.x, replace the binary (or run `docker pull`). If
 ## Fixed
 - OAuth resource indicators: Accept `imap`, `smtp`, `pop3` and `sieve` as valid resource indicators for OAuth access tokens.
 - PostgreSQL: Incomplete channel binding implementation.
+- JMAP: Return RFC-3339-conformant UTCDate literals in capabilities: min `0001-01-01T00:00:00Z`, max `9999-12-31T23:59:59Z`.
 - Reject invalid duration values (e.g. `1h30m`).
 
 ## [0.16.12] - 2026-07-06
diff --git a/crates/common/src/config/mailstore/capabilities.rs b/crates/common/src/config/mailstore/capabilities.rs
index 131ca9e9..500014a9 100644
--- a/crates/common/src/config/mailstore/capabilities.rs
+++ b/crates/common/src/config/mailstore/capabilities.rs
@@ -7,7 +7,6 @@
 use crate::config::mailstore::jmap::JmapConfig;
 use ahash::AHashSet;
 use calcard::icalendar::ICalendarDuration;
-use chrono::{DateTime, Utc};
 use jmap_proto::{
     object::{email::EmailComparator, file_node::FileNodeComparator},
     request::capability::{
@@ -84,8 +83,28 @@ impl JmapConfig {
             Capability::Calendars,
             Capabilities::Calendar(CalendarCapabilities {
                 max_calendars_per_event: None,
-                min_date_time: UTCDate::from_timestamp(DateTime::<Utc>::MIN_UTC.timestamp()),
-                max_date_time: UTCDate::from_timestamp(DateTime::<Utc>::MAX_UTC.timestamp()),
+                min_date_time: UTCDate {
+                    year: 1,
+                    month: 1,
+                    day: 1,
+                    hour: 0,
+                    minute: 0,
+                    second: 0,
+                    tz_before_gmt: false,
+                    tz_hour: 0,
+                    tz_minute: 0,
+                },
+                max_date_time: UTCDate {
+                    year: 9999,
+                    month: 12,
+                    day: 31,
+                    hour: 23,
+                    minute: 59,
+                    second: 59,
+                    tz_before_gmt: false,
+                    tz_hour: 0,
+                    tz_minute: 0,
+                },
                 max_expanded_query_duration: ICalendarDuration::from_seconds(86400 * 365)
                     .to_string(),
                 max_participants_per_event: bp
diff --git a/tests/src/jmap/principal/get.rs b/tests/src/jmap/principal/get.rs
index 29d1b2a4..218f3dca 100644
--- a/tests/src/jmap/principal/get.rs
+++ b/tests/src/jmap/principal/get.rs
@@ -105,7 +105,7 @@ pub async fn test(test: &TestServer) {
             "urn:ietf:params:jmap:calendars": {
               "maxCalendarsPerEvent": null,
               "minDateTime": "0001-01-01T00:00:00Z",
-              "maxDateTime": "65534-12-31T23:59:59Z",
+              "maxDateTime": "9999-12-31T23:59:59Z",
               "maxExpandedQueryDuration": "P52W1D",
               "maxParticipantsPerEvent": 20,
               "mayCreateCalendar": true