email stuck in draft

Hello everyone, nice to be with you! I have a problem with my exchange server 2016

I just installed exch 2016 in an environment where there was already exchange 2010. all mailboxes were successfully migrated to exchange 2016

and users can email each other from outlook desktop

but when we try to connect to OWA, we can only receive messages, but all sent messages go directly to draft.

the exchange server is used only inside our organization, it is not connected to the internet.

when I do a Get-Queue, I can see messages sent via outlook desktop in the queue but those sent via OWA are not in the queue. moreover when I do a test-mailflow, it fails. (failure)

can someone help me to solve this problem?