Nextcloud could not send message

After new installation of the whole Ubuntu server and Nextcloud, I can not send mails from nextcloud. But configuration seems to work, no error message.
And I can receive mails in Nextcloud, to it seems the dovecot is ok.
And sending from the CLI of the Ubuntu server, where also the Nextcloud is installed, works. So also postfix seems to be ok!
I also started debugging of Dovecot, but there are no errors…
But it works, when using my mailserver from other provider.
So it seems something happening internal, but I’ve no idea…

You will need to debug Postfix for sending mails, but not Dovecot. Dovecot only is responsible for handling incoming mails and mailboxes.

In many cases Postfix does not accept mails to be sent due to the sender’s domain name, which is missing in the as mydomain.
Please also keep an eye on the ports in If you want to send using ports 465 oder 587, a few entries in will need to be activated.

Very interesting. Turned on the debugging, then the mails were send.
Turned off debugging and now it still sends e-mails.

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