This problem has been covered many many times. Check archives.
On Tuesday, May 27, 2003, at 08:33 PM, Rob Francis wrote:
> I was happily using vpopmail 5.2.1 and qmailadmin. Everything was fine.
> However, our clients demanded some form of webmail access, so after
> trying a
> few packages, I settled for SquirrelMail (PHP pages that we could set
> to our
> needs). SquirrelMail requires an IMAP server for authentication and
> Courier-IMAP seems to be the fastest around and recommended by most
> Everything worked wonderfully EXCEPT for the fact that you could only
> authenticate about 3 times before getting a username/password unknown
> If I restart the Courier authentication daemon it works for another 3
> I even tried setting up a cron job to run a script as root that
> restarts the
> Courier authentication daemon every minute.
> The Courier IMAP list was the first place I searched for help but they
> adamant that the problem is with vchkpw and that I should upgrade to
> 5.3.20. I have done this but still have the same problem.
> Any suggestions? Has anyone else had this problem?