Exchange 5.5 SMTP settings

Ive scanned high and low for an answer to this question and I can now
see the 'end of the teather' moving closer, so I hope someone can help
me with this problem.
I have set-up Backoffice 4.5 (exchange 5.5 sp2) on a server with
popcon as a 3rd party pop retreival. All incoming e-mail is set-up fine

but Im having no luck sending out e-mails (im aware of the 'smtp is
better than pop' issue, and may well revert to this in due-course ,
however I really need to work out WHY this SMPT wont send out e-mails,
before moving on!)


The setup is as follows:


Domain/E-mail host: 1&1 (pop / auth.smtp)


ISP : pipex with dynamic IP (this will be moved to Tiscali with fixed
IP soon)


Exchange 5.5 sp2 (am intending to download sp4 today!)


Ive tried talking to 1&1 but theyre not much help, Ive tried inserting

the pipex DNS IP, 1&1 smtp IP and server name in the connections tab
(in the forward all/ dns dialog box) , but they will not work.


I would be most gratefull for any help here.


ALsun