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 -n

Chain 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

telnet mail.arquilog.com.br 26

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.

Try on your DO server

sudo ufw allow 26
sudo service ufw restart