All the domains i have configured are wroking fine via sqwebmail. but i am unable to use it via any email client
like Outlook Express.
Make sure you configure the email client to use the full email address as the username:
POP/IMAP user: [EMAIL PROTECTED]
POP/IMAP server: mail.domain.com
http://sniffter.com/ - info on the Sniffter hand-held Network Tester