Forum Discussion
Distribution Group External Senders Restriction
I have a distribution group under Exchange Server 2016 which should not receive mail from external users. I checked the option "Only senders internal to my organization"(see screenshot attached). But...
Hi, so we had a similar problem.
External contacts were able to send emails, to our internal distribution groups, even though we had the -RequireSenderAuthenticationEnabled $True.
So what we found out, was that in our exchange 2016, Under Mailflow / Receiving connectors. Our spamfilter server, was allowed to use port 25 as an external anonymous relay.
We removed it from the allowed list, and now the emails are denied from external contacts towards out internal distribution groups, as intended.
The reason (for our sake) was that our exchange server, saw everything received from the spamfilter, as an authenticated user, because of the above setting.
I hope this helps you.
BR
Martin
