23 Aug
2024
23 Aug
'24
5 a.m.
I would be grateful if someone could vet and verify (or guide otherwise) the following pattern please.
With the major mail vendors move to DMARC - Full Reject, I have a small challenge.
- We have a number of 365 Distribution List addresses.
- These lists accept email from anyone and, currently, then forward those emails onto list members.
- List members, however, are NOT necessarily email addresses within the list's mail domain. They might be outlook.com, Gmail, yahoo, Hotmail, username@local.ISP.
Consequently, DMARC Reject policies are causing these emails to be marked spam as the 365 Dist. List forwarding is not doing any header manipulation.
My thinking is:
- I could set up a Mailman list (elists.mydomain.com) alongside the 365 Exchange mail domain (mydomain.com)
- I leave inbound mail deliver to the 365 Dist. lists.
- I reconfigure the (mylist@mydomain.com) Dist. Lists to fwd to a similarly-named Mailman address at the email sub-domain (mylist@elists.mydomain.com)
- The Mailman list, by virtue of having to use the 365 MTA, should be able to accept all inbound from the list (mylist@mydomain.com).
- Mailman would then need to re-write the mail headers such that the inbound email to-be-forwarded from the Mailman list, both appears to come from the (mylist@mydomain.com) address, and also has the 365 'mydomain.com' SPF and DKIM records. And given Mailman has to use the 365 MTA, it would actually be coming from that main mail domain.
- Somewhere in there, the original sender's email address would need to be included, such that a Reply-to-All from a receiving List member would not only go back to the List, but also the original sender.
My thinking is that with this pattern, I don't need to worry about inbound emails to the list address as that would simply continue to function as normal, and fwdd mails from the List to recipient list members would not be marked spam as the headers would all be good.
Is my thinking good? Or am I out of my cotton-pickin' mind?