creating an smtp server
a few weeks ago, i wrote a bit about self hosting services. it got me wanting to write an smtp server because trying to self host all the services required is pretty insane. you need postfix for the smtp, then you need dovecot for imap access, then various “milters” like spamassassin, and lastly, all the other stuff to set up DKIM, DMARC, SPF, etc. it’s crazy.
so why write one from scratch? mostly just so i can practice writing software since at my dayjob i’ve been doing a whole heck of a lot more devops stuff (which is not fun for me). but also, email is interesting. it’s the only widely used federated, decentralized communication we use online. ie, you’re not punished or missing out if you don’t use gmail or hotmail. you can host your own or use any other email provider, and your email still works. anyway, so, i want to play around with that.
as for my second goal, well, it would be nice to make something that’s pretty simple to use. so, i’m going to try to lump everything together that i need and package it up in a nice little binary. there are other projects out there-one that i came across was stalwart. i installed it, but it’s very configurable. i got a little overwhelmed. that author definitely knows a thing or two about email, i would like to also know a thing or two.
so, that’s what’s going on there.
i got a little bit started and under way, but it’s a small amount of things. ie, HELO, MAIL FROM, RCPT TO, and DATA that writes the emails to a sqlite db.
as for next steps, i think one of the things i really need to do is to differentiate between connections coming from myself to send to others and connections from others delivering mail to me.
i think what i might do is that if i get a successful AUTH, then we’re sending mail which seems pretty simple.
if we don’t get an AUTH, then we’re receiving mail. after the MAIL FROM command, i need to parse out the domain, check its MX records, check that the domain from EHLO also matches the connection IP, and then check the SPF records. at least for this first pass, that might be enough…
anyway, i wanted to write that out to give myself a plan.