Why you should not run a mail server at home

Some hobby server admins like the idea to self-host their emails at home. Maybe because they don’t trust common e-mail hosts or they want to have full control over their hardware. Although this sounds reasonable at first, I do not recommend running a mail server at home.

I’m referring to German internet providers. The situation might be different in other countries, where you can get static IP addresses and proper PTR records.

Suspicious IP addresses

The mail problem here is that general purpose ISPs for consumers give you dynamic IP addresses with pre-defined PTR (reverse DNS) records. Both can cause big issues if you aim for acceptance regarding big mail providers such as Gmail, Yahoo and Hotmail. There is a simple reason for that: Big providers take IP addresses from consumer address ranges for suspicious, because they are not meant to be used for hosting purposes. If an e-mail from such an IP is received, there is a high probability, that this e-mail was sent by spam malware on a private PC. On the other hand, addresses from a hosting provider’s range are more trustworthy, because there is some sort of identity proof at almost every hosting company. If spam is received from one of these “trustworthy” IP addresses, the responsible person can be taken in charge quickly.

Popular e-mail providers check for these criteria:

  • Is IP-address from consumer range?
  • Is IP-address changing in time?
  • Is the PTR-Record different from the mail server hostname?

If the answer to one or more of these questions is “yes”, mails probably won’t be accepted or moved into the “Junk” folder. Unfortunately, for most internet providers, all three questions are true.