[Dovecot] Dovecot + Exim + Maildir quota problem

[Matteo Tinazzi]

Hi all i'm a new user of this list, i got a server with DirectAdmin 
which has exim as MUA, dovecot as POP/IMAP server, recently i added the 
quota to exim and pointed the maildirsize file in the same location if 
the dovecot's one so both services can interact with it. This has been 
done to let exim update the quotas while doing localdelivery while 
dovecot can show quotas through roundcube and update them when users 
delete mails.
The issue that i noticed is that some users get wrong quota 
informations... after a little investigation i think it could be a 
concurrent access to this file so dovecot tries to remove the deleted 
mails fomr maildirsize and exim tries to put new ones inside.
In a specific case i got a user with a quota of 50M seeing that 75% of 
his quota filled while the real weight of the mail files is about 4% ...

any help would be very appreciated