Existing nextcloud email user can send and receive emails new one not

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Just upgraded to 27.0.2 and enabled server encryption.
Today I generated a new user , at the first usage of mail credentials for the new user and its mail address have been asked and accepted.
but the new user cannot send or receive mails
tried with the Admin account of Nexcloud which I never used in mail so far and here the same
The admin account even having been the fist user to be activ before other users have been created and they are able to send and receive.

So from my point of view since a specific point in time activating the mail server in the users profil seems to not being able to send or receive even if existed from before

Tested the other way round and send from a former user inside nextcloud to the newly created ones. Send to several accounts external and internal all worked but the mentioned users above did not receive any mail
So the mail system is working ! but not for the newly created user.

Please if any one has an idea where to look send me the exact path and information’s I should show up

Thanks in advance

Any suggestion what could prevent newly created user from sending/receiving mails whereas older user still are able to send/receive mails?

Thanks in advance