Trouble Sending Email?
Technology with Integrity
By Tim Torian, Torian Group, Inc.
Are some of your emails bouncing, or just never arriving? Are people telling you that they can’t send you email? These are symptoms of the increasing security that internet providers are using to try to prevent spam.
If you have your own mail server, you may be experiencing some odd problems with some emails not getting through. Even if you don’t, you may be experiencing problems getting email from certain people.
To understand how email gets blocked, you need to know a little bit about how email works. When an email is sent, the sending server looks up the domain name of the destination email (yourcompany.com). It uses the domain name to ask your Domain Name Server (DNS) what the name of the destination mail server is. It then looks up the IP address of this server. Finally it packages the email message into a series of Internet packets and sends it to that address. Part of the address of a mail server is a “port number”. Ports are a way to tell which incoming information goes to which program on the same pc. Think of it like the apartment number for a building. One port is for email (port 25), another for web sites (port 80).
Internet providers have gotten much stricter about forwarding or receiving email from unknown email servers, to help prevent spam. In fact, they do a number of things:
1. They keep a list of known spammer names and addresses. If your email comes from one of these, it will be dropped. This is known as blacklisting, and there are tools to check to see if your server is blacklisted. The problem is that some lists are blocking entire providers such as Comcast, based on the idea that they sell service only to home users. One solution is to forward mail through a known (unblocked) mail server at your ISP.
2. An ISP may block all traffic on port 25 that does not come from their own servers. The way around that is to contact them and have them make an exception for your address, or get permission to forward your email through their server. SBC/AT&T and WirelessTCP require this. All your email goes directly to their email server, and then out to the destination.
3. The destination server may look up the source address of the email, and see if it matches the domain name in the email. One of the big ways spammers hide themselves is by faking the source of the email. If the email doesn’t match, the email server receiving the message either drops it, or sends back a message to the source server requesting that it be resent. For this to work, your server IP address has to be listed correctly on the internet. In some cases this can be set up incorrectly, causing mail to be blocked.
4. Another recent variation on this is the use of “SPF” records. This is a special entry in the Domain Name Server that specifies what email servers could legitimately be sources for email for that domain. Many Internet providers are making this a requirement, including AOL. If you are able to send to some places, but not to AOL addresses, this may be the cause. You will need to have your DNS provider or computer consultant add an SPF record to your Domain Name Server.
The battle to prevent spam is escalating. It is estimated that the cost of spam is over $4 Billion per year. As security tightens, you may need to implement new features to keep your mail flowing smoothly.
Tim Torian has taught computer networking at the College of Sequoias and Cal Poly Extension. He has a BS in Computer Science, and has been consulting on computer networks for the past 20 Years. His industry certifications include: Cisco CCNA and CCNI, Microsoft MCSE, and Novell CNE. He is president of Torian Group, Inc. which provides a full range of Technology Consulting services to local business, including computer services, networking, and custom software development. They can be reached at (559) 733-1940 or on the web at http://www.toriangroup.com