So I’ve been running self-hosted email using Mailu for a couple of months (after migrating out of Google Workspace). Today it turned that although my server seems to be capable of sending and receiving emails, it also seems to be used by spammers. I’ve stumbled upon this accidentally by looking through logs. This seems to have been going on for all this time (first “unknown” access happened just a couple of hours after I’ve set everything up).

While browsing the logs there were just so many crazy things happening - the incoming connections were coming through some kind of proxy built-in to Mailu, so I couldn’t even figure out what was their source IP. I have no idea why they could send emails without authorization - the server was not a relay. Every spammy email also got maximum spam score - which is great - but not very useful since SMTP agent ignored it and proceeded to send it out. Debugging was difficult because every service was running in a different container and they were all hooked up in a way that involved (in addition to the already mentioned proxy) bridges, virtual ethernet interfaces and a jungle of iptables-based NAT that was actually nft under the hood. Nothing in this architecture was actually documented anywhere, no network diagrams or anything - everything has to be inferred from netfilter rulesets. For some reason “docker compose” left some configuration mess during the “down” step and I couldn’t “docker compose up” afterwards. This means that every change in configuration required a full OS reboot to be applied. Finally, the server kept retrying to send the spammy emails for hours so even after (hypothetically) fixing all the configuration issues, it would still be impossible to tell whether they really were fixed because the spammy emails that were submitted before the fix already got into the retry loop.

I have worked on obfuscation technologies and I’m honestly impressed by the state of email servers. I have temporarily moved back to Google Workspace but I’m still on the lookout for alternatives.

Do you know of any email server that could be described as simple? Ideally a single binary with sane defaults, similarly to what dnsmasq is for DNS+DHCP?

  • markstos@lemmy.worldEnglish
    2·
    8 months ago

    I hosted email professionally for over a decade… and I can’t recommend getting back into the business. At that time we were using Qmail, although I also have experience managing Exim and Postfix. About 90% of incoming email remains spam.

    For outgoing email for things like server cron mail, a stub service like msmtpdcan be used to receive local mail and forward it to to a local service.

    To receive and host email, Fastmail is good.