ISP services


If you don't find an answer here... please feel free to contact us directly.

Why does my DSL provider block all SMTP servers except its own? (Port 25 blocking - outbound mail not functioning)

smtp outbound email - CardinalFactor.NetAnswer:
Some DSL providers block all traffic (incoming and outgoing) through port 25, except for their own SMTP servers to avoid being being blacklisted for spam (junk e-mail).

We provide outbound SMTP accounts for laptop users. Where ever you are -- with Internet access you can securely send email.

A common feature of SMTP servers is open-relaying. Open-relaying allows anybody on the internet to relay an email message through an SMTP server. The disadvantage of open-relaying is that it makes all messages appear to originate from the relaying server. For this reason, open-relaying is usually disabled because a spammer could use an SMTP server with an open-relay to send spam, and it would appear that the owner of the SMTP server is sending the spam instead of the spammer. This makes it very difficult to trace the origin of the spam and stop it.

If a DSL customer were to operate their own SMTP server, it is possible that it may be configured improperly with open-relaying enabled, and have spam relayed through it. In this situation, it appears that the DSL customer is sending the spam. So to avoid this situation, the DSL provider ensures that no customer can operate their own SMTP server, and blocking port 25 effectively does just that.

One of the disadvantages of this arrangement is that it also prevents the use of any SMTP server other than those of the DSL provider. If you are experiencing outbound email problems then you must set your outbound mail server as instructed by your DSL provider. Your outgoing mail will still appear with whatever e-mail address you have designated in your account settings.

Port 25 blocking does not affect incoming email through POP3 servers, which do not use port 25.

What are the POP/IMAP account settings?

server - mail.CardinalFactor.Net
User ID | Password - see your account information

I'm at home where my ISP is (my local cable co.) and I send an email via my account to another user. Will my email be blocked because Postfix will not find my account on a mail server?

If you are at home and have configured your pop account to use as both the incoming and outgoing mail server then this will be no problem at all. It's dependent upon your email client setup as you must specify which account to "send" from if you have multiple pop accounts. I often work from my home office -- even with our servers located in downtown Toronto -- and do just that. This of course depends on whether blocks port 25 for its users. If this is the case, we can provide alternate ports for SMTP traffic.

Still Need Help?

First Name
Last Name
Phone Number
Your Comments and Questions

CardinalFactor.Net ISP   |   xguru, Inc. web design   |   BWareSoftware Inc. application development
© 2001 - 2016 CardinalFactor.Net. All Rights Reserved.