>yes, they want this email - it is a confirmation of their transaction

You  still  didn't  answer  me  re: what kind they're requesting. Both
types  are  tricky devils.

DSNs  are  RFC-standardized  and  are generated by servers' Postmaster
(<>)  accounts,  but  the  process  of  requesting  one is tricky. The
otherwise-deprecated   Return-Receipt-Requested:   header   is   often
interpreted as a DSN request by servers that support DSNs.

MDNs  can  be  even harder to track down; they are to be sent out from
mail  clients,  but  are  not  subject  to  any  one  RFC.  Though the
Disposition-Notification-To:  header  is  usually  treated  as  an MDN
request, the format for the outgoing MDN varies a lot.

You need to look at an incoming message with the receipt request in it
and  look  for  the relevant header. Then you also need to look at the
full  source  of a receipt that does make it out--or, if necessary, in
the  outbox  before it's sent--to make sure the MUA isn't futzing with
the  headers  in any way (i.e. truncating or munging the To: address).
Many  MUAs  don't  even put MDNs in Sent Items so you can look at 'em,
which I think is very poor design.

A  possible roadblock in a different area is DSNs erroneously sent out
from  <MAILER-DAEMON>, which is not a guaranteed-acceptable MAIL FROM:
for  servers  that  do  sender  verification.  The null (<>) sender is
always  acceptable,  as is <Postmaster>, but other unqualified senders
do  not  need to be accepted...ironically, perhaps, the reason servers
send out from <MAILER-DAEMON> is usually as a "safety measure" in case
badly  configured  remote  servers reject <>, but the failsafe ends up
being the exact opposite!

Sandy


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