IMAP UID Unique across all Mailboxes

Hello Manager

We have installed Microsoft Exchange Server 2010, In that we have multiple mail boxes installed.

Can I consider that UID generated for each emails in the all mailboxes remain unique? We are storing all emails information in one database for all the mailboxes so need to verify can we use UID as primary key?

UID mean, Through OpenSSL I am running command . FETCH 8119 (UID)  to get unique number.

Thanks

Mehul Khatri