This tip is for customers running dedicated exchange and MT, though it will probably raise in hybrid scenarios as well.
In this scenario the MX record is sending the traffic to MT environment and the transport rule is based on isMemberOf.
Description : If the message:
Is sent to a member of group 'email@example.com'
and Includes these words in the message subject: 'Recognition Summary'
and Is received from 'Outside the organization'
Take the following actions:
Set audit severity level to 'Low'
and Delete the message without notifying the recipient or sender
and Stop processing more rules
and Send the incident report to firstname.lastname@example.org, include these message properties in the report: sender, recipients, subject, cc'd recipients,
bcc'd recipients, severity, sender override information, matching rules, false positive reports.
The transport rule was firing for all group members except a single user, Alex.
Alex mailbox resides in ANSI and Exchange had no issue to resolve Alex’s external address but then fails to lookup the external address in the address book.
The address book lookup is looking for a proxy address for Alex@mgd.contoso.com but that was missing so the solution was quite simple, add the external address to the proxy address attribute.
Service Engineer II