Underscore in domain is accepted

[orlitzky]

Prelude> :m + Text.Email.Validate Data.ByteString.UTF8
Prelude Text.Email.Validate Data.ByteString.UTF8> isValid $ fromString "local@exam_ple.com"
True

While underscores are legal in DNS, they're disallowed for hostnames. So you can't have either an 'A' or an 'MX' record for a name with an underscore in it, and thus no address with an underscore in it will be deliverable.

This is a gray area with respect to RFC5322, but I think it's best to reject them since in practice the addresses are invalid. A quote from the RFC:

Note: A liberal syntax for the domain portion of addr-spec is
given here. However, the domain portion contains addressing
information specified by and used in other protocols (e.g.,
[RFC1034], [RFC1035], [RFC1123], [RFC5321]). It is therefore
incumbent upon implementations to conform to the syntax of
addresses for the context in which they are used.

[Porges]

This is basically the same thing as issue #2; RFC5322 is very loose with regards to domain names. My eventual intention is to add stronger validation for this based upon another package rather than including the code in email-validate, as domain parsing/validation has more widespread usages.

[orlitzky]

Ok, sounds good. I just wanted to mention it because email-validate was failing the underscore test I developed for an old ruby validator I wrote. I left that test commented out for now.

[orlitzky]

Thanks! I'll update my tests.

[Porges]

Note this is not yet published to hackage. I'm thinking that it is going to be 3.0 as it breaks compatibility with existing addresses.

[orlitzky]

Not a problem. I have a tool email-validator that uses email-validate for its syntax checks (which are a huge part of the program). I have no other reason to make a version bump, so I can wait and then update the version bounds to make sure my test suite passes.

On a related note, I also wrote a domain name parser in the meantime for harbl but I never finished the project. It's not dead per se, I just have other things to do... The goal is to parse DNS blacklist names which are essentially domain names. Someday, if I finish it, I can try to split out the domain name parsing into a library.