Sorry for sneaking in this thread, but it might be a reason for a
patch on the Apple side.
Up until 10.3.9 Server, and 10.4 Client, I used to be able to create
users with short name containing a dot. The latest OS doesn't allow
that easily (there seem to be some not so clean workarounds), but the
closest thing I can do is to create the primary short name with
another character in place of the dot (for instance an underscore) and
add an extra short name with the dot as I want it.
Now, if I use PAM for authentication dovecot will not permit using the
alternative dotted short name as it will seem to fail authentication.
I do not remember exactly what is the issue, but I can do a test if
you like. Other servers seem not to have an issue, just dovecot.
Perhaps it is just an issue when interacting with PAM.
Giuliano