I gave all details, answered all questions and despite that the problem is not solved and they closed the ticket saying that I should check my firewall... which I left open during the tests.
I don't know what else to do... Ticket #588076.
Maybe search for another sawslution?
Maybe you could actually tell us the problem?
This isn't a place for complaining about support as this is the community forums.
Sorry for that.
Simply put, from my droplet I can't connect to port 26 of my mail server (not on DO). Yes, the SMTP server runs on a non-default port.
If I telnet that server on port 26 from the droplet I get no answer. I flushed all the rules and set the default policy of iptables to accept.
The same tests run on another provider works perfectly. So I don't think it's the SMTP server fault.
Here are the tests...
From the droplet:
iptables -L -nChain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Trying 138.128.178.18...
telnet: Unable to connect to remote host: Connection timed out
From another provider:
telnet mail.arquilog.com.br 26
Trying 138.128.178.18...
Connected to mail.arquilog.com.br.
Escape character is '^]'.
220-murdock.hmnoc.net ESMTP Exim 4.89 #1 Mon, 25 Sep 2017 14:26:09 -0400
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
quit
221 murdock.hmnoc.net closing connection
Connection closed by foreign host.