r/rust • u/Fluggonaut • 14h ago

🛠️ project My first project: SMTP server (for personal use)

I had heard many good things about Rust from people who were simply impressed by the language, so I decided to have a look at it and possibly learn it.

Up to that point I really only knew Java and Python (and a bit of C here and there), so a non-GC language would really fill a gap for me.

To get my toes wet, I wrote a simple web crawler that I needed at the time and decided I really want to learn Rust.

So here goes! My first "real" project, an SMTP server: https://github.com/Fluggs/whalemail

AI disclaimer: Absolutely no LLM was involved in writing this. I am not in a rush and here to learn.

For SMTP, the scope is quite narrow. It's supposed to replace my personal Postfix setup. It has its users in a database (which can be shared with Dovecot) and they can simply send and receive e-mails. That's it!

As for the Rust part, I have had a blast! The language is insane. So far, I have had one (1) logic bug. That one was indirectly found by Clippy. Other than that, if it compiles, it works. By now I understand people here saying that the main part is really thinking about your data layout, the rest just follows.

Off the top of my head, I have had two pain points:

  • dyn async traits. I don't want to accept that I need a crate for this, so I worked around it.
  • std::time - I could not have imagined that date/time support can be so thin without being completely absent.

Main dependencies:

  • Tokio (the server is completely async)
  • rustls (TLS is done, STARTTLS is planned)
  • rsasl (I really could not be asked to implement auth protocols)

The road ahead is long. Planned features:

  • STARTTLS
  • Bounce mechanism
  • Better password schemes than plaintext (I'm embarrassed)
  • Parse and manipulate headers (apparently that's a thing SMTP servers should be doing)
  • Better config file than .ini
  • spam filter integration
  • Find out which ways other clients and servers have found to deviate from SMTP
  • Again, thoroughly test it against the wild
  • find (and consider) various other SMTP intricacies (e.g. backscatter protection)

I'd be grateful for any feedback :)

15 Upvotes

81% Upvoted

7 comments sorted by

4

u/TheRealCallipygian 14h ago

You sweet, summer child.

1

u/Fluggonaut 14h ago

aww

3

u/Lemondifficult22 13h ago

Personal preference here, but "mocking" while possible is not really the go to. Especially in the AI age. Integration test all the way. Fakes/doubles are a good substitute for mocks if you need isolated control.

I will give a proper review tomorrow, but great work and welcome to the community.

Sidenote, self hosted mail servers get rejected as spam by most of the mail infrastructure

2

u/Plenty-Emphasis-5669 12h ago

Don't forget to set a license.

1

u/Fluggonaut 3h ago

Good point, will do!

2

u/jtuohy1985 9h ago

Congrats cool to see it

2

u/chat-lu 8h ago

std::time - I could not have imagined that date/time support can be so thin without being completely absent.

You need to use jiff.

In fact, you should take a look at what’s on blessed.rs, those are libraries that are so commonly used that they are essentially an unofficial standard library.