I've managed to install postfix, it works, when i am logged into my VPS as root I can send and receive mail fine. But the problem is i cannot connect with thunderbird or outlook. I also cannot telnet to the machine remotely on port 25. But i can telnet to it on port 25 when i am logged into the VPS. I know port 25 is open because sending and receiving email works. Even though it works i still opened port 25 in iptables. I am new to this and thinking this is some kind of DNS issue, but i don't know enough to figure out where the problem is. Can anyone help?

By the way my DNS settings are as follows:

Type=A record host=* Value=server ip address
Type=A record host=@ Value=server ip address
Type=A record host=www Value=server ip address
Type=MX record host=@ value=mail.example.com 10
  • 2
    Why are you trying to connect to port 25? Mar 1, 2016 at 4:54

2 Answers 2


Make sure the Postfix server is configured to listen on the public or all interfaces by editting /etc/postfix/main.cf

inet_interfaces = all

Also, Thunderbird/Outlook should be using
outgoing: Secure SMTP port 465 or 587
incoming: IMAP port 143 or 993 IMAP/TLS

Regarding the DNS; make sure it doesn't still say mail.example.com

  • thanks for replying. I have tried those ports as well and it says connection refused. Does that mean i need to open the port, or is that some kind of TLS, SSL issue? Mar 1, 2016 at 5:14
  • is the postfix server listening on the public interface?
    – Tim Penner
    Mar 1, 2016 at 5:24
  • ok this might be where the problem is. I tried lsof for port 465 and it didn't return anything. Where would i need to open this up, in iptables? Again i am new to this, so trying to solve the problem and understand whats going on at the same time. thanks. Mar 1, 2016 at 5:30
  • I added the following lines to iptables: -A INPUT -p tcp -dport 465 -j ACCEPT -A OUTPUT -p tcp -dport 465 -j ACCEPT But it still gives the same error Mar 1, 2016 at 5:36

Outgoing traffic over port 25 is commonly blocked by consumer ISP's, corporate, government and college networks etc. to prevent their users from transmitting unauthorised e-mail and SPAM.

You solve that either by using the outgoing mailserver your ISP offers in your email client or by having postfix listen to a second port in addition to TCP/IP port 25 and configuring your clients such as thunderbird to use that. TCP/IP reserved port for mail submission, 587, is a common choice, as is port 465 for SMTP over SSL.

Uncomment in your master.cf:

#submission inet n - n - - smtpd


#smtps     inet  n       -       -       -       -       smtpd

And opening those ports in your firewall.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.