saved by16 people, first byGarrett Pendergraft on 2007-12-03, last byCheryl Allin on 2008-05-27
- Reverse DNS — It’s crucial to ensure you have RDNS set up for every IP you deliver email from. RDNS involves a receiving mail server looking at the IP address your email is coming from and then checking to see if there is a registered domain associated with it. It’s a requirement for most receiving mail servers and whitelists, so don’t overlook it.
- Valid mail headers — The information contained in your mail headers is crucial to a receiving mail server deciding if they will accept your email. Make sure you’ve got a valid return-path (where bounces are sent), the correct MIME-Version and encoding information, DomainKeys/DKIM signature and your IPs in the received lines have RDNS set up. I’d also recommend checking out the list-unsubscribe header currently supported by Windows Live Hotmail.
- Throttling your delivery speeds — different ISPs have different maximum speeds you can send at. Once you start to exceed these speeds, they’ll consider you a spammer and start blocking you. Make sure you set a reasonable speed limit on the number of connections and messages you send per hour so you don’t tread on any ISPs toes. From experience most ISPs will allow a few hundred simultaneous connections and 25 or so messages per connection.
- Stay off blacklists — While your sending reputation continues to become more important, you still need to make sure you don’t appear on any major blacklists. Even if you’re following all the guidelines I’ve mentioned above, a rare blacklisting can happen to the best of us. I recommend checking the free Spam Database Lookup provided by DNS Stuff as often as you can. You can also apply to be whitelisted by ISPs such as AOL and Yahoo.
- Monitor all abuse accounts — By default some anti-spam systems (and people) will send any spam complaints to abuse@yourdomain.com. Make sure it’s set up and is actually going to someone responsible for your sending reputation. If a complaint is made, resolve it immediately. Don’t forget to register your abuse accounts with abuse.net.
