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When sending out emails with a MAIL FROM address > 81 characters I receive bounce messages from some MTAs:

501 Syntax error - Badly formatted address. (in reply to MAIL FROM command)

As soon as I change the MAIL FROM address to <= 81 characters, the MTA accepts my message.
I didn't find any limits in the RFC docs.

Is this expected behaviour or is the recipients' MTA misconfigurated?

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Please don't forget to accept the answer. – sebix Mar 1 '15 at 14:46

Accoding to the answers given at

The answer is 254 according to RFC 5321

So, those MTA are badly configured.

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That's the length of a valid email address. Maybe it have something to do with the SMTP protocol or a different restriction though? – horen Jun 4 '14 at 14:29
No, it has not. A SMTP server is magically required to actually acccept valid email addresses, or? How else would it work? – TomTom Jun 4 '14 at 14:30
You're right of course. Thanks for your answer. – horen Jun 4 '14 at 14:40

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