Login problem - specific ISP username policy

[regres]

Hi

I've just installed RC on my shared host and it seems to work fine
Unfortunately my ISP has kinda annoying email login policy.
Currently I have to login into RC (or any other webmail) using email username that looks like 'account.username'. The 'account.' part is always the same, only thing that changes for every email address is 'username' part.
So, here is my question - what should I do to be able to use only 'username', instead of 'account.username' for every login?
I was told that it's possible to change something in one of files concerning login procedures to make it work. Unfortunately I don't know PHP

I'd be grateful for any suggestions
Regards
regres