Authentication-Results header info not getting cleared on end-of-data/RSET

[cmadamsgit]

When qpsmtpd has SPF/DKIM plugins enabled and adding info to the Authentication-Results header, it appears that having multiple messages received in a connection just keeps appending to the AR header (rather than resetting after each message). For a connection that receives even two messages, this means a bad AR header; for a connection that runs longer with a bunch of messages, the header itself runs too long.

It looks like the SPF/DKIM results data is being stored as connection data, where it should just belong to a single message transaction.

[cmadamsgit]

I believe this is the correct fix:
#322