This is an IMAP server implementation written in Rust. It originally started out as a class project in Fall 2014. There is also an LMTP server attached so that SMTP servers may deliver mail without modifying the maildir themselves.
The most confusing thing for those reading the code who are unfamiliar with rust will likely be &str and String. &str is an actual string while String is actually a StringBuffer. &x[..] is used to get a &str out of a String called x and y.to_string() is used to get a String out of a &str called y. Sometimes we need something which is neither of these to be a string so we use .to_str() or .to_string() as appropriate. Sometimes we need a String but the thing we have can only be converted to &str so we have to chain the calls like so: .to_str().to_string(). It sometimes also occurs the other way around in which case we wind up with something like &z.to_string()[..].
& denotes a pointer (ie: pass-by-reference semantics). When you see &mut it means that the pointer is mutable. Rust only allows one mutable pointer at a time and enforces this at compile time. However, multiple immutable pointers may be created. * is used to dereference a pointer. In most cases, method calls will automatically dereference when needed.
The statement return thing; is equivalent to thing (note the absence of a semi-colon).
That should be everything someone who doesn't know rust needs to understand this code and why we do things certain ways.
IMAP has three states: unauthenticated (before log in), authenticated and selected. The most important commands for actually reading mail are log in, to get to an authenticated state; list, to get the list of folders; select, to get to the selected state; fetch, to get data and metadata about the messages; and store, to modify the flags (metadata) of the messages.
RFC 3501 - IMAP4rev1
RFC 2822 - Internet message format
RFC 2033 - LMTP
RFC 2821 - SMTP (LMTP is based heavily on SMTP)
RFC 2045 - MIME Part 1
RFC 2046 - MIME Part 2
Grab rust v0.12
Grab cargo
Run cargo run (alternatively, if you just want to compile the program, run cargo build)