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(KBID5568) PGP-signed messages get corrupted during scan

When Bitdefender scanning is activated, VSAPI MIME parser splits the messages in its constituent elements, before passing them one by one to the antivirus. On some Exchange servers, the repacked message is converted to a standard 7-bit encoding, corrupting in the process the inline PGP key. This is a flaw in the current MIME parser implementation in Microsoft Exchange.

For example, in the sample sent message (1), the MIME header Content-Transfer-Encoding has the value quoted-printable and the charset to us-ascii. When Bitdefender scanning is activated (2), Content-Transfer-Encoding is reduced to 7bit, while the charset becomes iso-8859-1.
The VSAPI MIME parsing modifies the MIME headers