Score:0

Port 25 blocked for *some* connections, not all

mz flag

I've been trying to set up an email server with Postfix and Dovecot. I wanted to test it with mail-tester.com but the email wouldn't get through. Emails still get delivered to my business email address (hosted somewhere else). The thing is, I can't even connect to port 25 of mail-tester.com or outlook.com.

Trying telnet from my server gives different results for Google and MailTester. Telnet also hangs when connecting to Outlook.

$ telnet gmail-smtp-in.l.google.com 25
Trying 142.251.2.27...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
...
$ telnet reception.mail-tester.com 25
Trying 94.23.206.89...
  (hangs, never connects)

I've never encountered this weird behaviour before. Trying nmap <IP> on my server is also strange: port 25 is shown as open when connecting from my home network but is blocked when running through a VPN. My hosting provider is Frantech (BuyVM).

in flag
Many ISPs will block certain ports due to the horrific abuses of spammers in the 90s and early 00s. You will want to call your provider and see if they are blocking. If they are, you will need to ask if they can disable the block. Most hosting providers operate like this, including AWS and Azure
ec flag
**Welcome to the Ask Ubuntu community.** In order to better diagnose your issue, please edit your question to include the version of the Ubuntu OS that you're running. Thanks
AnFi avatar
us flag
How long have you waited for SMTP greeting message? DNS problems with reverse DNS may cause 75 seconds delay. AFAIR some sendmail problems with aliases caused 10 minutes delay. It may be some problem with application level firewall. If you finally get the greeting message then **exact** delay may provide a valuable hint.
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