[Dovecot] How Can I Add New Flags

Hi all,

I am new in Dovecot. I wanna use Dovecot in the big mail system about 4 million active or passive users. We use recently Courier Imap, but search mails process is so slowly. I tried Dovecot that it is better then Courier so much. But I have a problem with integration Dovecot to my system. I am using some extra flags in mails to mark them from others. For example I use a private flag "M" to understand it that this mail come from us as newsletter. I make some changes in code, but unfortunately I could'nt add this flag to Dovecot correctly. Please help me it that how can add this flag.

I use maildir type

Thanks, Sezai