Connection refused - connect(2) for

I have the UCS5.0 server with OpenProject installed, right. It is not configured to any specific domain. Just the local pattern it automatically creates.
I have configured on my local machine a local docker smtp server called mailcow.
I added my localhost ip to the site “”.
I did a smtp test with python and it worked normally sending smtp under and I received normally.
I configured my smtp in openproject as shown in the image.
Occasionally, messing with the settings within the Univention console, I identified an email configuration and added my domain, as shown in the image.
I thought this would solve my problem, but it didn’t.
I checked that my server time was late, I thought that might be the problem too, but it wasn’t.
I can ping from inside the vm and it hits my localhost.
So when I send a test email, it gives the error below:
Checking the mail.log output, I got the following error:

Dec 22 23:10:19 ucs-5462 postfix/smtpd[6532]: connect from localhost[]
Dec 22 23:10:19 ucs-5462 postfix/smtpd[6532]: disconnect from localhost[] helo=1 quit=1 commands=2
Dec 22 23:10:19 ucs-5462 postfix/pickup[3489]: F196F4861CC: uid=0 from=<root>
Dec 22 23:10:19 ucs-5462 postfix/cleanup[6539]: F196F4861CC: message-id=<20221223021019.F196F4861CC@ucs-5462.xpto.intranet>
Dec 22 23:10:19 ucs-5462 postfix/qmgr[1433]: F196F4861CC: from=<root@ucs-5462.xpto.intranet>, size=714, nrcpt=1 (queue active)
Dec 22 23:10:20 ucs-5462 postfix/local[6541]: F196F4861CC: to=<systemmail@ucs-5462.xpto.intranet>, orig_to=<root>, relay=local, delay=0.02, delays=0.01/0/0/0, dsn=2.0.0, status=sent (delivered to mailbox)
Dec 22 23:10:20 ucs-5462 postfix/qmgr[1433]: F196F4861CC: removed

What could it be?