November 8th, 2010
No, I’m not talking about spam. Depending on the type of customers you host on your servers, they may have to send out bulk mails to their customers. If they’re not careful, they could get you’re server’s IP address blacklisted! This would be an inconvenience for you, and for the other customers you are hosting on the same server. Lets take a look at a few steps that can help you avoid that.
Allow only mail server to send out mail.
Only the mail server should be able to connect to port 25 of remote servers to send mail. You should not allow your customers to run scripts that connect directly to the remove server to deliver the mail. You can check a previous post of mine to find out how to do this.
Space out the mails
Once you are sure the customers are only using your mail server to send the mail, you will be able to control its flow. Limit the number of mails that can be sent per hour. Most mail servers monitor traffic from IPs and if it finds a prolonged burst in the number of mails from a particular IP, it will block or deferr mails from that IP. If this happens, you should have your mail server configured so that it processess the queue at appropriate intervals.
Something many mailers do not do. Most mailing list software also provide the option to process bounce back messages. Depending on the type of failure, those accounts are removed from the mail list, or mails not sent to that account for a specified period of time. So make sure your customers configure their mailing scripts to also accept and process bounce back messages.
Inform concerned authorities
If a majority of the members of the list use a particular mail service, check their website for their bulk sender guidlines. This may require you to give them details about the types of mails you are sending, and maybe a copy of one of the mails. Making sure you follow these guidlines will help prevent your server from being listed as a source of spam. Getting blacklisted means mails to other mail services will also fail. Work with your customers to provide all necessary information to these authorities.
About the Author:
Hamish joined Bobcares in July of 2004, and since then has grown to be well versed in the Control Panels and Operating systems used in the Web Hosting industry today. He is highly passionate about Linux and is a great evangelist of open-source. When not at work, he keeps himself busy populating this blog with both technical and non-technical posts. When he is not on his Xbox, he is an avid movie lover and critic