[HowTo] Replace courier with dovecot

[aseques]

@ merykonil
This is certainly not a mysql issue, mysql data in this case already has the _ci collation, so the select would be case insensitive.

It's failing for this check (on line 40)
if ($username =~ /^(([a-z0-9\-_]+\.?)+)@(([a-z0-9\-]+\.?)+)$/) {

So we could change that and it would work straight out of the box, I'd like to know the opinion of the dev guys, because this is probably done to mimic courier auth (wich reads the info from files and probably doesn't work either).
Also what happens with postfix and auth to send mail, does it work with caps there?