Hello community,

I use Mailcow on my Debian Stretch virtual server and it works great in itself - sending email works perfectly via Outlook, Apple Mail and webmail.

But since a previous update (I’m not sure if it was Debian or Mailcow) the sending of emails via the CommandLine on the same server using SSMTP a has stopped working.

The command…

ssmtp recipient_email@example.com
To: recipient_email@example.com
From: myemailaddress@example.com
Subject: test email

hello world!

…returns: ssmtp: Cannot open mail.example.com:587

I have already tested various settings in /etc/ssmtp/ssmtp.conf (TLS on or off, port 25 or 587):

root=myemailaddress@example.com
mailhub=mail.example.com:587
#mailhub=mail.example.com:25
rewriteDomain=mail.example.com
FromLineOverride=YES
#AuthMethod=LOGIN
AuthUser=MYUSER
AuthPass=MYPASS
UseSTARTTLS=YES
#UseTLS=YES
TLS_CA_Dir=/usr/share/ca-certificates/mozilla/

The file /etc/ssmtp/revaliases:

root:myemailaddress@example.com:mail.example.com:587
sax:myemailaddress@example.com:mail.example.com:587

Unfortunately, none of my settings lead to success 😖

The ports:
netstat -tulpn | grep -E -w ‘25|80|110|143|443|465|587|993|995’

tcp6       0      0 :::25                   :::*                    LISTEN      19239/docker-proxy  
tcp6       0      0 :::443                  :::*                    LISTEN      988/apache2         
tcp6       0      0 :::993                  :::*                    LISTEN      19301/docker-proxy  
tcp6       0      0 :::995                  :::*                    LISTEN      19285/docker-proxy  
tcp6       0      0 :::587                  :::*                    LISTEN      19201/docker-proxy  
tcp6       0      0 :::110                  :::*                    LISTEN      19331/docker-proxy  
tcp6       0      0 :::143                  :::*                    LISTEN      19317/docker-proxy  
tcp6       0      0 :::80                   :::*                    LISTEN      988/apache2         
tcp6       0      0 :::465                  :::*                    LISTEN      19227/docker-proxy

It can be reached via Telnet…

telnet mail.example.com 587

Trying <<IP>>...
Connected to mail.example.com .
Escape character is '^]'.
220 mail.example.com ESMTP Postcow

Sending works via other MTA, but not via SSMTP.

Could someone help me or give helpful tips?

Thanks in advance
sax