[cobalt-security] Domain of sender address does not resolve

[loptson@xxxxxxxxxxxx]

I'm seeing a lot of these types of messages in my logcheck output. We've noticed a slow down in the server as well.  I have a couple of questions:

1) are these anything to worry about?

2) will the attempts by the server to resolve the unresolvable slow things down?

3) if the answer to 2 is yes, is there a way to turn off the check and is that advisable?

The background is that I think I tweaked some settings that had to do with making sure that when folks said they were coming from a particular place that they really were.  Unfortunately I neglected to take good notes so I don't know what I tweaked (some TCP file where you set the contents to 0 or 1 strikes a bell).  The server is very slow and I wanted to see if we could speed things up a bit.

Thanks,
Paul


Jan 28 18:01:12 www sendmail[12952]: g0T017U12952: ruleset=check_mail, arg1=<kujarek@xxxxxxxxxx>, relay=[213.134.143.66], reject=451 4.1.8 <kujarek@xxxxxxxxxx>... Domain of sender address kujarek@xxxxxxxxxx does not resolve 
Jan 28 18:01:20 www sendmail[12953]: g0T01FU12953: ruleset=check_mail, arg1=<kujarek@xxxxxxxxxx>, relay=[213.134.143.66], reject=451 4.1.8 <kujarek@xxxxxxxxxx>... Domain of sender address kujarek@xxxxxxxxxx does not resolve