Forum Discussion
550 5.7.1 RESOLVER.RST.AuthRequired; authentication required
I work with a hybrid environment where almost all of the user accounts are now 365, but there are still some distribution lists that have not migrated yet. I have a particular on-prem Exchange 2010 ...
mailboxes in exchange online are in a different organization than recipients in your exchange onprem.
That doesn't change the fact that two of the three can send to the distro, while the one cannot. I don't see any differences in the three accounts, but maybe I'm not looking in the right places?