Reverse DNS needed on client's end for e-mail sending?

[peruda.com]

Hello all,

Quick question about reverse DNS. I know my server must have rev DNS configured for SMTP to work properly, but am I correct in thinking that my client must have reverse DNS on their DSL/dial-up/whatever connection in order to send through my SMTP server? I have a few clients who have tried everything and are still unable to send. I found this in /var/log/exim/mainlog (some info blocked for privacy):

2005-01-04 22:36:39 1Cm4mT-000J03-M7 <= customer@example.com H=(LAPTOP) [195.174.X.X] P=smtp X=TLSv1:RC4-MD5:128 S=26891 id=004c01c4f2f1$517133f0$6500a8c0@LAPTOP
2005-01-05 11:09:25 no host name found for IP address 195.174.X.X

When I do an nslokup on 195.174.X.X, it returns "Non-existent host/domain" - Could this possibly be the reason why they can't send?

Thanks so much!
-John

[dezignguy]

Reverse dns isn't necessary for clients sending mail through your server (unless you changed the settings to require something so restrictive!)

Are your clients using smtp auth to send mail? ie, logging in with their login in order to send?