When Alice@External is composing a new mail, after she types part of a name and selectes a recipient (the "To" field is populated and the name is underlined), have her double-click on the name in the "To" field. This should show a popup with the full email address under the name.

Finally an update on this situation. And maybe an understanding of why it's happening precisely with two different firms in particular.

One of the client/partner companies finally had their IT person look a little deeper. It turns out that they had our engineer in their internal system, and with the wrong domain. Once that was removed, everything seems to be working.

Also a bit more discussion yielded that these companies had added our guy to their Teams group essentially with his own separate log-in as if he were internal. I recall this causing some issues with Teams at one point, as our guy has to log out as himself and in as his entity for them. I didn't have enough info to put it together, but that's probably exactly where the bad info is stored. If they set up the Teams stuff in 2020 while we were figuring out how to operate under COVID, we didn't change domains until 2021. The only odd thing is that this was something that never came to the surface until we finally decided not to renew the old domain.

We're seeing if the other company can get their IT person to really get in there and look for our guy's info.

At least, finally, something.

Thanks for all your help and suggestions, Hornblower. The main struggle was getting someone at the other companies to really take a look and not just presume the issue was on our side.

Best regards,

Ann