A SMTP problem: when email receiver is more than one person which are saprated by ";", the smtp will dump the mail to badmail folder with no reason. But ok for one email address. "The specific error code was 0xC00402C7" in BDR file and "Delivery to the following recipients failed.
firstname.lastname@example.org; email@example.com" in BAD file
P.S both email addresses are valid, and can be sent if one receiver.