here is a good 2 tips for sendmail:
first we will add a throttle for sendmail to max 10 connetions per second.
#cd /etc/mail
open sendmail configration file ( sendmail.mc ) with your favorite editor and add this line:
define(`confCONNECTION_RATE_THROTTLE',`10')

then save the file and close it.

now we have to generate a sendmail.cf  file

m4 sendmail.mc >/etc/mail/sendmail.cf

restart sendmail.

2- second we gonna hide sendmail version when someone connect to port 25.
#Connected to 192.168.1.1.
Escape character is '^]'.
220 host.domain.net ESMTP Sendmail 8.13.1/8.13.1; Thu, 10 Nov 2004 06:01:39 +0300 (AST)

open file submit.cf and search for " O SmtpGreetingMessage=$j Sendmail $v/$Z; $b "
then replace it with this line:
 

O SmtpGreetingMessage=$b

then save the file and close it.

now restart sendmail and try to connect to port 25.

#Connected to 192.168.1.1.
Escape character is '^]'.
220 Thu, ESMTP 10 Nov 2004 06:04:34 +0300 (AST)

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