[Extra] Email header / address parsing

[Timo Sirainen <[e-mail]>]

Hi,

I was reading https://www.usenix.org/system/files/sec20-chen-jianjun.pdf and started wondering if IMAP should be handling some of this better. Especially for generating ENVELOPE. We could even still have time to add recommendations to IMAP4rev2?

For example:

1) Errors while parsing the address syntax: I was wondering if it would be a good idea to indicate this by appending .INVALID suffix to domains of all of the addresses in the ENVELOPE reply? That way it would be at least clear that something is wrong. Otherwise different implementations could always do something slightly different when encountering errors, leading to trust problems. For example could be done with these kind of addresses:

 - From: [e-mail] <[e-mail]>
   --> either: [e-mail]
   --> or: [e-mail]
 - From: <[e-mail], <[e-mail]>
   --> either: [e-mail]
   --> or: [e-mail]
   --> or: [e-mail], [e-mail]

2a) Space preceding the first header name
2b) Space after From header: Again
2c) Folding space before ":"
Not sure what exactly to do about all these. Don't parse these as valid headers? Or parse but append .INVALID for ENVELOPE? But that would work only for ENVELOPE headers.

3) Multiple From lines: Add all of these to ENVELOPE, as if they were all in a single From line.