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We're on Office 365/Exchange Online. We just completed a domain move from domain-old.edu to domain-new.edu. The .EDU TLD exclusive registrar (EDUCAUSE) is pretty strict about how long you can have two .edu domains - and we have another 5 months from here. The new domain is set up in Office 365, and everyone's primary SMTP is username@domain-new.edu, with a secondary of username@domain-old.edu. They're happily receiving mail for both addresses right now.

My dream is to be able to apply a transport rule that stamps a disclaimer on inbound messages sent to username@domain-old.edu that says something along the lines "This user used your @domain-old.edu address - please remind them to update their records, as @domain-old will stop receiving mail on October 15th, 2020" or so.

I've tried a few rules so far - recipient domain is @domain-old.edu, header To includes @domain-old.edu, but no luck yet. Any ideas on how to accomplish this?

I do already have 1 disclaimer rule in place to alert a user to "External Messages" for SPAM/Phishing Purposes.

Thank you in advance!

SteadH
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According to my research,if a message is not sent to recipient's primary SMTP address, the address will be resolved to the primary one when the message reaches Exchange server. We can't determine which addresses is used originally. This is a reason why we cannot create a transport rule to meet your request.

Joy Zhang
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  • Well, the exchange server is the place the alias is stored. Does that change anything? – SteadH Aug 09 '20 at 03:03
  • As far as i know, there is nothing change, a primary email address is usually the email address a user was assigned when account was created. And user sends email to someone else, their primary email address is what typically appears in the From field in email apps. They can also have more than one email address associated with their account. These additional addresses are called aliases or called proxy addresses. A proxy address lets a user receive email that's sent to a different email address. Any email message sent to the user's proxy address is delivered to their primary email address. – Joy Zhang Aug 11 '20 at 07:41