[ale] Odd network behavior

[David Corbin]

I've been having a problem for sometime that I'm at a bit of loss to 
figure out.  I have one Windows box (use by she who must be obeyed) that 
is "challenged" with regard to sending email.  She's using Thunderbird, 
and *sometime*, when send an email, the status dialog "sending email" is 
left on screen for 'a long time' (~30 seconds).  It usually succeeds 
eventually.  However, sometimes (< half the time), it's nearly 
instantaneous. It seems like it might be a DNS problem, but EVERY time I 
try to diagnose it as a DNS problem (using ping), it has no problems.  
I've also tried "telnet smtp 25" without any problems.

More info on my set up.
I'm running exim 4 on  linux box, which is sitting on the far side of a 
Linux firewall (i.e., to the server, the address has been NAT-obscured)
It's *possible* this problem happens for other clients on my LAN behind 
the firewall, but I use KMail elsewhere so it's not visible.

Any tips or ideas?
David