Can't parse email where Message-ID has more than one "@" character

Hi!

I've noticed that if Message-ID (or any other header using msg-id) has more than one "@" character than parsing via `parseMsgID()` from `header.go` fails with:

`missing '>' in msg-id`

as it expects to `consume()` special chars in the fallowing order: < , @ , >

i.e.

`Message-ID: <113c01d86b4a$53bb4230$fa9e45a$@appmanager@yahoo.com>`

I'm not sure if using two or more "@" characters in msg-id is correct but I've already seen a few of this headers in the wild.