MailScanner v4.85.1-1

[Lev Nagdimunov]

Hi Andrew,

You should be able to replicate the issue as follows: setup Exim (my server reports Exim version 4.84 #2) as the MTA to only process incoming email, set it to defer all incoming email. Setup mailscanner to process email in Exim's spool (ie, set incoming queue dir in Mailscanner to the spool_directory location in Exim's configuration). Normally you would then set Outgoing Queue Dir to the spool_directory of a second instance 
of exim (with a different configuration that does not defer), which would actually deliver the mail then (to replicate the issue you don't need this step). If you check the -D file (Exim's email data portion) in the Outgoing Queue Dir (before the second exim delivers any email in there), you will find that if your email was Base64 encoded, and some Base64 encoded lines (after they were encoded) were longer than 60 characters then Mailscanner will change the message in such a way that the full Base64 string is preserved but each line is formatted to be 60 characters instead of whatever it had been before. This will break any DKIM key, and if its being forwarded by the second Exim (which also needs SRS enabled for this to work even without a DKIM key generally) then most freemails at least will reject the message (e.g. Yahoo, Google, Hotmail, etc). 

Thank you,

   Lev
 		 	   		  
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