postfix virtual domain on etch

[cakar]

I have a mail server up and running sending and receiving mails with one primary(dom1) and a virtual domain(dom2). My problem is that i get the header anyUserOfDom2 at dom1.tld when i receive mail on my gmail account which i sent myself from user at dom2.tld . So the part after the at sign should be dom2.tld but i get dom1.tld so people can't send replies.
Any help extremely appreciated as it's been around a week i started having trouble adding the second domain.
Thnx in advance.

[HelpQuick]

How are you sending the message? are you using an email client on another machine?

[cakar]

Using the email client it's ok, but when try to send it through the browser (domain2.tld/squirrelmail) it has 1stDom.tld appended.
Do I have to use its own mail server for the outgoing mails from web interface to have their own domain names?
Should I set up an mx dns record for each domain to have their mail working or can i just use the one I created the 1st place, namely mail.dom1.tld, and could it be related to that web interface outgoing mail with wrong domain appended problem?