MailScanner & DoS

[Devon Harding]

For some reason, I can't seem to stop hackers from performaing DoS against
my IPCop fw & MailScanner server.  I get alot of these in my
/var/log/maillog and the boxes get locked up:

Mar  1 20:12:48 mars sendmail[27017]: k220vlXF027017:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
Mar  1 20:12:48 mars sendmail[27019]: k220vmrk027019:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
Mar  1 20:12:48 mars sendmail[27018]: k220vlM8027018:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
Mar  1 20:12:49 mars sendmail[27020]: k220vm8s027020:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
Mar  1 20:12:49 mars sendmail[27023]: k220vngJ027023:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
Mar  1 20:12:49 mars sendmail[27021]: k220vmjG027021:
69-165-202-64.miamfl.adelphia.net [69.165.202.64] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA

What can I do?
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