The display name that preceded the address, with quoting and comments removed, or undefined
when the address had none.
The name of the RFC 5322 group the address appeared in, if it appeared in one.
The address as normalizeEmailAddress produces it, for string comparisons. This is
undefined when the address is not a valid RFC 5321 mailbox, which a header may legitimately
contain: root@localhost is a well-formed RFC 5322 address but has no fully qualified
domain.
Compare addresses through this property rather than through full, which preserves whatever
casing and quoting the sender used. Note that a quoted-string local-part may itself
contain an @, so read a receiving domain from the last @ rather than the first.
A single mailbox read out of an RFC 5322 address list header.