IMAP authenntication problem

IMAP question:I have configured a new Lotus Domino server 6.5.3 on Linux Suse 9.2.

If I configure on the security tab of this server

Internet authentication: More name variations with lower security

I can logon to the http server AND to the IMAP server both with

my username AND shortname/Userid

If I configure on the security tab of this server

Internet authentication: Fewer name variations with higher security

I can logon to the http server AND to the IMAP server ONLY with

my username AND NOT WITH shortname/Userid

The question is : which is the function of

Ports–>Internet Ports–>Mail–>IMAP

Enforce server access settings: No

???

Until I had a Lotus Domino 5.xx version the meaning of this setting was:

If I configure on the security tab of this server

Internet authentication: Fewer name variations with higher security

and Enforce server access settings: NO

I can logon to the http server ONLY with username

and I can logon to the IMAP server both with username and shortname/Userid

Why this is no more true on version 6.5.3 ?

There are a lot of “imap client” or “imap gateway” (as Squirrelmail I am using)

that on linux platform do not like name with spaces in the middle as a username

generally is

thanks in advance,

Andrea