consider localhost as invalid domain

[bigio]

fix issue #254

[marcbradshaw]

question, should localhost be considered valid for DMARC?

It is called in 3 places

lib/Mail/DMARC.pm
48: croak "invalid envelope_to" if !$[0]->is_valid_domain( $[1] );
54: croak "invalid envelope_from" if !$[0]->is_valid_domain( $[1] );
60: croak "invalid header_from" if !$[0]->is_valid_domain( $[1] );

I would argue that foo@localhost in the From header is an invalid header_from

RFC7489 6.6.1 states

o Messages with an RFC5322.From field that contains no meaningful
domains, such as RFC 5322 [MAIL]'s "group" syntax, are typically
ignored.

I would argue that @localhost is not a meaningful domain in this context.

we should also lc $domain before checking, to account for @localhost etc.

It may also be worth covering .localdomain here too?

[bigio]

localhost case fixed, should @localhost.localdomain be a valid domain in RFC7489 context ?

[msimerson]

localhost case fixed, should @localhost.localdomain be a valid domain in RFC7489 context

Nope. I think a general rule might be, "if the domain doesn't resolve to public IPs, it's invalid."

[msimerson]

we should also lc $domain before checking, to account for @localhost etc.

It turns out, I already have a commit for lower casing in my local repo. Landing soon in #256