All these old RFCs

For p25.dev I was researching a feature. Customers who don’t have a static IP address, or sit behind a firewall they can’t control, should be able to use p25.dev’s backup MX too. I try to be standards compliant as much as possible, so I researched existing solutions.

In 1999, the ON-DEMAND MAIL RELAY (ODMR) RFC 2645 was proposed. It allows an SMTP client to tell the server “let’s switch roles, I am the server now”. Probably the RFC still speaks for many email self-hosters:

With the spread of low-cost computer systems and Internet connectivity, the demand for local mail servers has been rising. Many people now want to operate a mail server on a system which has only an intermittent connection to a service provider. […] However, systems with dynamic IP addresses (which are very common with low-cost connections) have no widely-deployed solution.

The world of RFCs entertains me. I already explained some details of an IMAP RFC. Whenever I have a question about SMTP, DKIM, DMARC or any of the email related standards, I don’t need tutorials or dedicated literature. The RFCs are so nicely written that they are my primary resource.

Unfortunately, ODMR does not fit p25.dev’s current architecture. Its implementation would be a major redesign and ODMR has a couple of security implications. The search continues. I just like that for most problems in computer systems, a solution has been discussed a long time ago already.