SMTP greetings for Sendmail security

SendmailIt is the most widely used email sending/receiving proxy in Unix environments. Because the sendmail mail server is characterized by powerful and complex functions, we should send the SMTP greetings to do some security work.

When sendmail accepts an SMTP connection, it sends a greeting message to the machine, which is used as the identity of the host, the first thing it does is to tell the other party that it is ready.

Edit the "sendmail. cf" file (vi/etc/sendmail. cf) and change the following line:

O SmtpGreetingMessage = $ j Sendmail $ v/$ Z; $ B

Changed:

O SmtpGreetingMessage = $ j Sendmail $ v/$ Z; $ B NO UCE C = xx L = xx

Now manually restart the sendmail process to make the changes take effect:

[Root @ deep] #/etc/rc. d/init. d/sendmail restart

The above changes will affect the flag information displayed when Sendmail receives a connection. You should replace "xx" in the "'C = xx L = xx" entry with your country and region code. The subsequent changes do not actually affect anything. However, this is a legal practice recommended by the "news.admin.net-abuse. email" newsgroup partners.

By reading the above article, we can easily find that the security of Sendmail is worth our attention, while understanding SMTP greetings greatly improves its security performance.