exim4 configuration

Hey,

I have never had a need for a mail server but this time round I thought I'd set one up.

I have exim4 installed on debian 6

phpmail function works fine

I can also send mail from the console

However I want to receive mail also.

I have multiple domains but I want to use one as the main mail server, so let's say:

domain1.com

so I want an email for the main mail server admin[@]domain1.com

but I want to forward my other domains i.e admin[@]domain2.com & admin[@]domain3.com to my main email address admin[@]domain1.com

I also want to be able to access admin[@]domain1.com via an email client like thunderbird using IMAP.

how do I go about setting up exim4 to do this? or is there a noobs guide that someone knows of?

Also, when I added my domains via the linode dns manager it adds an MX record for all my domains:

mail.domain1.com

mail.domain2.com

etc…

do I delete the mx records for all domains except domain1.com?

I know this is a basic question, but I have been trying to setup my main account but keep getting: 550 550 relay not permitted (state 14) when trying to send to my main email address.

Thanks in advance..