KMail not able to authenticate

[Anne Wilson]

After what feels like a long struggle I've got my new CentOS mail server 
running to the point where I can run KMail on the same box and see all my 
messages.  Unfortunately, when I try to read the  messages from my netbook I 
am told that authentication method LOGIN is not supported by the server.

The dovecot configuration file has the line

disable_plaintext_auth = no

which always allowed login on the old system.   Any ideas where I need to look 
for this?

Anne