Simple Mail Transport Protocol (SMTP) is the underlying technology that acts as the foundation for email delivery. In simple terms, it is the language that mail servers use to communicate with each other and to move email messages across the Internet.
According to Wikipedia, 78% of all email messages are spam. As a consequence, mail servers must constantly evolve to try to stay ahead.
If you operate your own mail server, there are a number of potential risks you may face:
- Excessive email message delivery attempts by spammers or other illegitimate users could consume significant bandwidth and processing power on your mail server.
- Any security issues with your mail server software (such as buffer overflows or injection vulnerabilities) could compromise the integrity of your entire mail system.
- If your server is hosted on a cable or DSL broadband connection, there is a chance that your ISP is blocking port 25 (the SMTP port) in an attempt to prevent spammers from using your network. This would render your server useless as it would no longer be able to receive mail.
An SMTP cloaking service works by placing one or more public SMTP servers in front of your own mail server. Public servers receive all mail destined for your domain, perform necessary anti-spam and antivirus checks, and only pass mail to their own mail server if the message appears to be good.
This arrangement offers some considerable advantages:
- The outside world does not have direct access to your mail server; they don’t even know what kind of mail server software you’re running.
- Your bandwidth is reduced, since only those messages that have passed the tests defined by the public servers will be delivered to your own server.
- You can run your mail server on a port other than 25, perfect if your ISP is one of those that blocks connections to port 25.
- A good SMTP cloaking service will provide multiple public SMTP servers, giving you additional redundancy in case one of your servers goes down.
- If your own server is down for any reason, the public SMTP servers will hold mail and automatically forward it to your own server when it’s back up, providing you with a mail backup system and ensuring you never lose any email as like. result of problems with your own mail server.
There is a potentially significant drawback to using an SMTP cloaking service:
If the cloaking service doesn’t have a list of all valid users in your domain, it will have to forward every mail it receives to your server, regardless of whether the recipient exists or not. Some SMTP cloaking services will allow you to provide a valid list of mailboxes on your domain; this is certainly a worthwhile exercise, as it allows public servers to reject any mail sent to non-existent recipients. However, you will need to think about how you will update this list each time you add a new user to your mail server; it’s probably best to discuss this with your SMTP cloaking service provider, as the procedure will be different for each provider.
Choosing an SMTP Cloaking Service Provider
- You should expect to pay between £40 and £60 ($55-$85 USD) per year per domain, depending on the features and support provided. Some companies may charge more for premium levels of support or additional features.
- Beware of limits on the amount of email traffic and whether additional charges will be incurred for excessive email volumes or bandwidth usage.
- Does the service allow you to specify a list of valid mailboxes in your domain? And if so, how often can it be updated?
- Does the service include any anti-spam or antivirus measures? While anti-spam solutions can help reduce spam, those that are too sensitive may unknowingly reject legitimate emails.
If you have any questions that are not covered in this article, my best advice is to contact different SMTP cloaking service providers to discuss your own specific requirements. Everyone’s needs are different and the potential benefits you could get from having an SMTP cloaking service will depend on your individual circumstances.