Email RFC for duplication
July 8, 2014 12:35 PM   Subscribe

Is there any sort of official documentation about not sending duplicate emails if the same email address appears more the once on the To/CC/BCC lines?

Obviously, my entire experience with all email programs has shown this to be the case, but I'd love to see if there is any official documentation perhaps in the form of an RFC or other internet cite that proves this. Maybe it is just common sense and happens on the email client level. This is hard to search for because of so many other duplicate email problems people have. Thanks for any pointers!
posted by gatorbiddy to Computers & Internet (3 answers total) 1 user marked this as a favorite
I couldn't find anything in the RFCs about duplicate recipients, and it's likely that the exact behavior is client/server-specific. Gmail, for instance, returns
250 2.1.5 OK, duplicate recipients will be consolidated. p8si31788579icv.22 - gsmtp
if it's given a duplicate RCPT address.

Hotmail doesn't indicate whether it consolidates addresses in its responses, just returns status 250 for each instance of a valid address.

An attempt on another mail server resulted in 250 OK for each address, and only one email delivered to that address. Duplicates in the DATA headers were preserved, however (but this might be corrected on the sending side by a mail client smarter than telnet).
posted by WasabiFlux at 2:26 PM on July 8, 2014

section 3.6.3. "Destination Address Fields" of rfc5322 is the current spec for how the To/Cc/Bcc fields should be interpreted, and it says nothing about de-duping recipients.
posted by russm at 5:23 PM on July 8, 2014

Thanks for the answers!
posted by gatorbiddy at 12:12 PM on July 9, 2014

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