[Dovecot] pop3-login: Internal login failure (auth failed, 1 attempts)

[Frank Bonnet]

Hello

I have a user that experience troubles with it's pop3 client (eudora)
at random time/hour the dovecot server refuse the connection to his
machine during several  minutes then it restart normally to download its emails ...

the message is like the following :

dovecot: Oct 09 15:36:35 Info: pop3-login: Internal login failure (auth failed, 1 attempts): user=<xxxxxxx>, method=PLAIN, rip=147.215.50.48, lip=147.215.1.3, TLS
dovecot: Oct 09 15:41:35 Info: pop3-login: Internal login failure (auth failed, 1 attempts): user=<xxxxxxx>, method=PLAIN, rip=147.215.50.48, lip=147.215.1.3, TLS
dovecot: Oct 09 15:46:35 Info: pop3-login: Internal login failure (auth failed, 1 attempts): user=<xxxxxxx>, method=PLAIN, rip=147.215.50.48, lip=147.215.1.3, TLS
dovecot: Oct 09 15:51:35 Info: pop3-login: Internal login failure (auth failed, 1 attempts): user=<xxxxxxx>, method=PLAIN, rip=147.215.50.48, lip=147.215.1.3, TLS
dovecot: Oct 09 15:56:35 Info: pop3-login: Internal login failure (auth failed, 1 attempts): user=<xxxxxxx>, method=PLAIN, rip=147.215.50.48, lip=147.215.1.3, TLS

I run dovecot 1.1.4 (compiled on the machine) onto a debian etch 64 bits machine (IBM X3650)

The passwd is memorized by the client so it is not a typo error of my (experienced) user
who is a Computer science professor.

Thank you