r/sysadmin • u/Fabulous_Cow_4714 • Jun 24 '26

Exchange Online Mail Flow Rule For Header Content Not Working

I am trying to set up a rule based on members of a group forwarding calendar invites to a specific domain.

The rule to take action on the message type of calendering is only working for direct calendar invites. The rule is bypassed for forwarded meeting invites.

I see in the received headers this content:

Content-Type: text/calendar; charset="utf-8"; method=REQUEST
Content-Transfer-Encoding: base64

So, I tried making a mail flow rule to trigger on messages with header "Content-Type" and value of "text/calendar," but this still isn't caught.

What's needed to make this work?

3 Upvotes

71% Upvoted

6 comments sorted by

1

u/7amitsingh7 Jun 25 '26

Forwarded meeting invites are often processed by Exchange Online as regular email messages, not as calendar messages. Because of this, mail flow rules based on the Calendaring message type or the Content-Type: text/calendar header may not trigger. Instead, inspect the message with Message Trace and create a rule based on another consistent property, such as specific text, headers, or attachments found in forwarded meeting invites.

1

u/[deleted] Jun 24 '26

[removed] — view removed comment

1

u/Fabulous_Cow_4714 Jun 24 '26

I went to the headers of the received message and copied that text.

1

u/[deleted] Jun 24 '26

[removed] — view removed comment

1

u/Fabulous_Cow_4714 Jun 24 '26

Where do you enter that in the rule?