[cobalt-users] Help? - Email Problem (RAQ2)

["Lee Brookes" <cob@xxxxxxxxx>]

I have most of my sites set up on individual IPs. However some less
important sites (my own non-commercial web sites) share a single IP.

I have just discovered something which has left me rather baffled.

If I send email to any of the virtual accounts which are on a shared IP 
using my own email client software it arrives in the correct mailbox 
without a problem - (the email is forwarded using a ctach-all forwarding 
address).

However if I use a perl script (on another server altogether) to generate 
and send an email to an email address at one of the web sites sharing an 
IP it simply never arrives - nor does it seem to bounce back.

I know the script is OK because I can get it to send to web sites on the 
same server (which have their own IP) without a problem.

I am desperatley trying to make some sense out of this.

1) I know the perl script will send out email ok
2) email sent by the perl script is received/forwarded on/by the same 
server to web sites which DO have their own IP.
3) email sent from my desktop client to a website with a shared IP 
DOES arrive OK - those sent via the perl script do not.

Is it possible that the sendmail programme which is actually sending the 
email from the perl script is actually doing some kind of authentication 
check before sending the email - or am I completely off-base.

All and any suggestions as to where to start to look to try to solve this 
would be appreciated.

Regards
Lee