Hello SmarterTools Support Team
We are running SmarterMail Enterprise with Exchange integration (EWS) in the latest available version. Our users are using eM Client as their mail client (latest version). We have identified two reproducible bugs in SmarterMail's EWS-to-iTIP conversion when generating outbound calendar notification emails.
ENVIRONMENT
- Server: SmarterMail Enterprise
- Protocol: Exchange Web Services (EWS)
- Client: eM Client
- Timezone: Europe/Berlin
BUG 1: Duplicate ATTENDEE entries in outbound METHOD:CANCEL iTIP messages
When a calendar event or recurrence occurrence is cancelled via EWS (eM Client), SmarterMail correctly processes the EWS operation internally but generates outbound iTIP notification emails (Content-Type: text/calendar; method=CANCEL) with every ATTENDEE listed twice. This is non-compliant with RFC 5545 and RFC 5546, and causes incorrect rendering in recipient mail clients (duplicate participant entries displayed in the event notification UI).
This was observed in two separate cancel operations:
- Cancellation of a single occurrence (RECURRENCE-ID based cancel, SEQUENCE:5) of a recurring series (UID: 952287e1-f63b-4766-a2bf-03c15b342fb2)
- Cancellation of a single occurrence (SEQUENCE:2) of a newly created recurring series (UID: 888ad85d-d4db-429f-a3c2-4a8b0d2df209)
In both cases the duplicate ATTENDEE entries appeared only in the outbound iTIP mail. The EWS operation itself appeared correct.
BUG 2: Redundant / logically inconsistent EXDATE in outbound iTIP when terminating a series via UNTIL
When a recurring series is terminated by updating its recurrence rule with an UNTIL value (via EWS), SmarterMail generates the outbound METHOD:REQUEST iTIP notification with both:
- RRULE: ... ;UNTIL=20260324T235900 (series ends before the next occurrence)
- EXDATE:20260325T083000Z (explicitly excluding that same next occurrence)
The EXDATE is logically redundant and inconsistent: since the series already ends via UNTIL before the excluded date, the occurrence cannot exist in the first place. SmarterMail should not be adding an EXDATE for occurrences that are already outside the UNTIL boundary. This suggests the EWS-to-iTIP translator is combining two separate operations (occurrence cancel + series termination) without checking for logical conflicts.
Observed on UID: 952287e1-f63b-4766-a2bf-03c15b342fb2, outbound REQUEST SEQUENCE:6.
ADDITIONAL OBSERVATION (not necessarily a bug, but worth noting)
When a new recurring series is created via EWS while a previous cancel operation's iTIP notifications are still in transit to recipients, the new series is immediately visible in the organizer's EWS calendar. This causes the organizer to perceive the event as "reappearing" and triggers a redundant second cancellation — resulting in multiple cancel emails to recipients within seconds. This may be an inherent EWS timing behaviour, but better handling or a short write-delay on the client sync side could mitigate user confusion.
Ticket 225-31559C2A-0031 - reported 3/24/2026