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Possible denial of service exploit

Version: ZMailer 2.99.49p9, compiled with gcc and bundled libresolv,
using system malloc	
Platform: Sun SparcStation 20 running Solaris 2.5

smtpserver receives mail from a non-RFC822-compliant SMTP gateway that
rewrites addresses as follows:

To: <user@mydomain> becomes
To: <"SMTP@gateway-name@Servers[<user@mydomain>]"@remote-domain>

When the router tries to process this message, it consumes all swap
space and pegs the uptime at 10; the hardware hangs afterwards.

Needless to say, the only work-around I've found is to create a policy
that states "rejectsource +" or "freezesource +" to the offending