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Should you turn off your network's outbound SMTP (port 25)?

Serdar Yegulalp
03.23.2006
Rating: -3.62- (out of 5)

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If you have an Exchange server that's allowed to open outbound SMTP connections in your network, should you block port 25 everywhere else in your network, since it's not really needed? The short answer is yes, and here are some good justifications:

I admit to being personally inconvenienced by having port 25 blocked on my personal network. I remotely administer a domain name that has its own SMTP sender, so I can send mail on behalf of that domain name.

After this restriction went into place, the only way I could send e-mail was through my ISP, and only by using the e-mail address my ISP provided. (If I tried to send e-mail with a @mydomain.com address through its mail relay, it would reject it and insist

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that I could only send e-mails with a @myisp.com address.)

Since they wanted to charge me extra for the privilege of being able to use port 25, I surrendered and just started using the @myisp.com address for the sake of simplicity. I don't like it, but if it means my ISP is no longer playing host to spammers and Sober-style worms, I can live with it.

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.

MEMBER FEEDBACK TO THIS TIP

I absolutely agree and recently implemented this on my network. I wish all SMTP traffic was from legitimate, registered e-mail servers.
—John A.

Do you have comments on this tip? Let us know.

Related information from SearchExchange.com:

Tip: Many ISPs now blocking port 25

Ask the Expert: Testing IP restrictions on port 25

The spamfighter's toolbox

On-Demand Webcast: Locking down Exchange Server

Learning Guide: How to fight spam on Exchange Server

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