Target Audience
Customers using Microsoft 365
Content
We have confirmed a specification change in Exchange Online within Microsoft 365 where, in the case of forwarding (redirect forwarding) where the envelope From is an external address and the email is sent externally, the envelope From address is rewritten and sent.
Sender Rewriting Scheme (SRS) in Office 365
[Post-change Envelope From Address]
<Forwarding Mailbox Username>+SRS=<Hash>=<Timestamp>=<Original Sender Domain>=<Original Sender Username>@<Forwarding Mailbox Domain>
Due to the above specification change, the envelope From address of the target email will be changed to the above format, and if <Forwarding Mailbox Domain> is an internal domain, there is a possibility that the filter will be applied as if the email is sent from an internal domain user.
Workaround
Regarding this feature, by creating a filter under the following conditions, it is possible to create a rule targeting emails whose envelope From address has been changed due to this phenomenon.
Examples of search strings are as follows.
If you need assistance with the settings, please contact HENNGE One Technical Support.
Please note that this workaround is based on the currently confirmed behavior, and if there are further specification changes in Microsoft 365 (Exchange Online) in the future, it may not behave as expected.
Search String
- Rule Condition: Match all of the following conditions (AND)
Target: Envelope Sender
Condition: Matches regular expression
Pattern: \+SRS=.*@