Fetchmail 6.3.5 and early 6.3.6 release candidates, when delivering messages to a message delivery agent by means of the “mda” option, can crash (by passing a NULL pointer to ferror() and fflush()) when refusing a message. SMTP and LMTP delivery modes are not affected.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/53511/fetchmail-SA-2006-03.txt
Source: https://packetstormsecurity.com/files/53511/fetchmail-SA-2006-03.txt.html