Originally Posted by amartlk
I have qmail toaster installed in centos5.3 and thunderbird as email client. i get duplicate mails of same user if he sending mail only once
Well, if you're being CC'ed more than once, or a reply is coming from an email list, then that's the correct behavior. You don't provide details about the email...have you checked the headers? Mail logs? Do you have clamav, spamassasin or other such things running??
Check your client's SMTP timeout value. If it's set too tight, it will occasionally timeout during an update, and cause duplicates.
And did you try to look this up?