How to solve the "The message could not be sent because it has unresolved recipients." in Outlook for MacOs? I keep getting the error msg "The message could not be sent because it has unresolved recipients." every time I sync my mail box:



I have tried different solutions like this one https://answers.microsoft.com/en-us/msoffice/forum/all/unresolved-recipients-message-prevents-email-to/4d79640c-60f6-49a8-9210-57c6e1c99fce with no luck.

Reading through the logs generated with log enabled option in Outlook brings no valuable information, I would need to know what recipient is really causing this (the error message could bring that along for my benefit, but hey, why would anyone think I would ever need that? :) ). 

Any ideas?

MacOs 10.14.6
Outlook for Mac 16.28
Looks like some destination e-mail address is wrong formmated (like: missing domain, or just some name without full e-mail address) 

I would check all the destination recipient address and validate them for syntax. It the case for checking syntax name@domain.com (formatting syntax). 

This is not because non-existing final destination mail, is just technically wrong formatted e-mail syntax addresses

Those messages seems to be on the outbox to be sent, stucked there because of that

Check Outlook outbox for queued messages to fix that.