Can't get SMTP with STARTTLS to work

Hi,

I have just installed Bitwarden on-premise and can’t get it to work with my SMTP server.
My SMTP server only works over port 587 with STARTTLS required and no matter what settings I use it doesn’t work.

I use Postfix and I have a valid certificate from Let’s Encrypt with the intermediate installed as well.
I use this SMTP server for about 50 other users and I have never had a problem with it until now.
It seems that Bitwarden doesn’t like something but I can’t find anything in any logs.

This is what I get from the SMTP server when Bitwarden tries to send an email:

connect from 1.2.3.4.isp.com[1.2.3.4]
lost connection after STARTTLS from 1.2.3.4.isp.com[1.2.3.4]
disconnect from 1.2.3.4.isp.com[1.2.3.4] ehlo=1 starttls=1 commands=2

I’ve changed the IP of course.

Does anyone have any idea what could be wrong? And if I can enable some debugging mode that let me see what Bitwarden logs when trying to send over SMTP?