Mails are allowed to have multiple addresses in the from header as
long as they also have a sender header. However, in basic testing, I
have yet to find a MUA that even displays multiple entries for from.
Has anyone seen such a user agent?
KMail (Linux MUA that probably not many people use - I don't) displays both of
them. Reply goes to both as well.
Gmail only displays the first one, but sets both addresses as Reply-To - even
if no such header was set.
Functionally, should multiple from
addresses be considered a deprecated feature?
Not sure. I am a little concerned about possible abuse of this feature though.
If your anti-spam/-phishing filter runs a check against the From address, does
it know how to interpret a From field "info(_at_)paypal(_dot_)com,
Virus Bulletin Ltd, The Pentagon, Abingdon, OX14 3YP, England.
Company Reg No: 2388295. VAT Reg No: GB 532 5598 33.