From memory Outlook Express/Windows Mail requests capabilities before
login (and never after login)?
I don't know about them, but I remember someone told me Outlook was
fine. The point anyway is that clients don't have to request anything,
the capability is pushed to them. There are two ways:
this was me, and dovecot 2.0 was still in alpha status... :)
Anyway, I tested Outlook only, not Outlook Express. There always were
some differences between those, so maybe they behave different with
login capabilities, too.
Regards,
Sebastian