Errors in the SMTPAPI header
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I am not sure if this is the right place to post this, but I have a mystery!
I’m using PMPro on a site and an email was sent to a user that their membership ended.
The site owner got a reply from SendGrid with the subject: Invalid SMTPAPI Header.
The body of the message said, “A message was received from this address by our systems that had errors in the SMTPAPI header, and cannot be processed due to the following:
– 2 duplicate to header detected, rfc5322 states that there should be a max of 1.”The only thing I can think of is that the email sent by PMPro has some kind of duplicate header.
Any thoughts? Thank you!
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