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Sending E-Mail on Today ’s Complicated Interwebs

Due to a recent issue with sending mail, I wanted to expand a little more on the complexities of sending mail. It's one of those things that seem like it should "just work", and yet in practicality that's not really the case. Years ago, port 25 was the port in which you connect with your email client and send mail on. Actually, port 25 is still the default SMTP port, but for many of you coming in from some of the largest ISP's both in the country and (to us) internationally, the only port 25 you can get to is the one that your ISP provides you. Some major ISPs known to do this are: AT&T, MindSpring, BellSouth, MSN, CableOne, NetZero, Charter, People PC, Comcast ATTBI, Sprynet, Cox, Southwestern Bell,, EarthLink, Verio, Flashnet, Verizon, MediaOne, Optus, Frontiernet... and yes, there are more. So, first, what is "Port 25 Blocking"? In a nutshell, it means that your ISP has instituted a block that prevents its users from sending outgoing mail via any third party mail-hosting services. Your domain hosted here is a third party mail-hosting services and so understanding that, depending on your choice of ISP, you may be prevented from using that aspect of your domain service by your Internet Service Provider. Before the chest thumping consternation begins, the fact is that the reason they do this is pretty sound. Disallowing connections to any other smtp port means that they have much less spam coming out of their network and if someone does try to spam from their network, it goes through mail systems that they have control over. They can institute software traps to catch spammers before they get out, as well as lock down infected computers on their network that have, usually unbeknowst to the user, become part of a botnet due to a virus infection. This block became much more prevelant after the MyDoom virus of 2004, which slammed mailservers the world over and those ISP's that had been dragging their feet found themselves implementing it in the MyDoom aftermath. They are trying to do the right thing - it is unfortunate, though, that in order to keep their network (and all networks) safer it limits what you as a legitimate user can do. So, how do you know if your ISP does this? Well, you can simply google your ISP name and Port 25 Block and you will likely find someone, somewhere that wrote about it. You can check the Terms of Service and it will likely state it somewhere in their policies. You can also simply call support and ask them - this isn't a secret, and they'll be happy to tell you. There are some alternatives you can try - you can switch to port 26 instead of port 25 and see if you can get to SMTP on our servers that way. You can also try port 587. As time goes on, these alternatives are less and less likely to work, and your best bet is to use your ISP's SMTP server - it won't affect the "from:" email address display to whoever you are sending to, and your ISP's ability to authenticate you is fairly simple, as you are a computer on their Network who has already authenticated. It should also be noted that by using these "workarounds", you're essentially violating the terms of what your ISP wants you to do and these aren't guaranteed to work forever. We've used the SpamHaus blacklists to block mail at "Exim's Level". What that means is instead of accepting all the mail that's delivered, then running it through many levels of processing, we refuse IP addresses that are in the Spamhaus blocklists. This greatly, greatly reduces the load on the server as the processing for the mail that we accept is actually the single highest resource usage hog on every server we have. Nothing that we do, or you do, is more resource intensive other than backups, and those only happen once a week. Mailscanner runs continuously. Previous to last week, only XBL and SBL (proven spammers and proven hijacked computers) were set as default blacklists in Exim.  cPanel switched to Zen, which also included the PBL list, and once that was added, some of you had problems. The Spamhaus PBL is a DNSBL database of end-user IP address ranges which should not be delivering unauthenticated SMTP email to any Internet mail server except those provided for specifically by an ISP for that customer's use. What this means is that if you have been "getting around" your ISP's rules by using port 26 or 587, the use of the PBL list will stop you from connecting to our server because by your Network's rules, you're not allowed to be doing what you are doing. You can find out if this affects you by
  1. Going to
  2. Finding your IP and then
  3. Seeing if it is in any of the Spamhaus Databases
If it is on the PBL List, you can request it's removal and the criteria are a bit lower than the other lists (XBL and SBL) due to the fact that it is an advisory list and not a known problem list. If you are on the XBL or SBL list, you have a bigger problem than we can go into here. Other alternatives are to simply use your ISP's SMTP server - which is what they want you to do, and what you really should be doing to comply with their rules. You can also switch to using GMail, which we described how to set up in an earlier article. If you need an invite, let us know.


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