GICT knowledge base

My SMTP port 25 is Blocked by my ISP

Published 22 October 2015

InterServer Web Hosting servers have opened port 25000 and 2500 for our customers who require SMTP services but their ISP blocks port 25.

This change will not affect current users that are able to use port 25. It allows the users who can not user it to have another port to connect to for the purposes of sending E-Mail.

ISP that block Port 25:

AT&T (can be unblocked at the request)
MindSpring
BellSouth
MSN
CableOne
NetZero
Charter
People PC
Comcast ATTBI
Sprynet
Cox
Sympatico.ca
EarthLink
Verio
Flashnet
Verizon
MediaOne

To manually test your mail server you can perform the following

Open a command prompt (start>run>cmd in windows 2000 or greater)
Type “telnet [your mail server IP] 25” don’t forget the port number – – – this will open an SMTP connection
Type “helo yourdomain.com” – – – server will respond “220 mx.mydom.com SMTP”
Type “mail from:<[email protected]>” – – – server responds “250 Address Ok”
Type “rcpt to:<[email protected]>” – – – server responds “550 not local host someotherdomain.com, not a gateway”
Type “data”
Type “subject:Some email subject”
Type “Text for the email body”

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