CentOS postfix smtp server connection refused from outside

user968898 asked:

I am quite stuck with my postfix/smtp configuration on my CentOS machine.

I setup a mail dns mail.domain.tld, configured in the postfix main.conf file and tested
locally on the server by connecting to

$telent mail.domain.tld 25

This gives me a response and it’s possible to send e-mails from the mail server it self.
Now, I want to use the mail server in my e-mail client but I cant get a connection with the server, if i test a telnet connection from my local desktop it’s been refused by the server.

I know this should be something like a firewall, there is iptables running but I added ports to be accepted, I added + saved + restarted iptables but no port 25 or 587 (also configured from the postfix master.conf) wont work from outside the server.

(telnet 587 also not working from the server locally).

# lsof -ni tcp:25
master  27179 root   12u  IPv4 52473467      0t0  TCP *:smtp (LISTEN)
master  27179 root   13u  IPv6 52473469      0t0  TCP *:smtp (LISTEN)

# netstat -an | grep LIST
tcp        0      0       *                   LISTEN      
tcp        0      0        *                   LISTEN      

# iptables -L
Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:smtp  

I can deliver more outputs if needed!

Thanks in advance

My answer:

You should be sending outgoing mail from your desktop on port 587, the submission port, not port 25 (which is meant for transferring mail between SMTP servers). Make sure your /etc/postfix/master.cf has the submission section enabled.

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