Support from Internet Connection

Recent SMTP Trouble, Secondary SMTP Port, and Spam

Sent: 2004/08/12
Audience: All Hosting Customers.

In the recent weeks we've received more and more reports from customers having problems sending mail through our SMTP services. The two most common error messages seen by customers are a "451 Blocked" error and a "Connection Refused" error.

The former is most often received when the customer's ISP has been blacklisted on one or more Real-time Blackhole Lists, or RBLs. The ISP is often submitted to these RBLs because someone received spam email from an IP address on that network. And as we currently subscribe to quite a few RBLs, and will continue to subscribe to more as part of our anti-spam measures, customers whose ISPs are listed will not be able to send mail through our services.

The latter error is caused by dial-up and broadband ISPs who have blocked access to port 25, the port SMTP traffic goes through, on any network but their own. Basically, when an Internet Connection customer is using one of these ISPs to access the Internet, they can no longer use the SMTP services provided by us.

There are two methods of getting past these issues;

First, you may simply change your mail client's setting to send through the SMTP server provided by your ISP.

Second, you may also try specifying another port for SMTP on our network. Per RFC 2476, we've now begun offering SMTP on port 587 in addition to the standard port 25. This port does not check against the RBLs that we subscribe but requires SMTP authentication just as port 25 has now for some time.

More info on Blacklists.

If you have any questions about this issue please feel free to contact the Internet Connection Support Desk:
Phone: 410-820-5678
Email: support@internetconnection.net
Toll Free (US resellers only): 800-203-5678

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