Seekable iterator implementation in Zend_Mail_Storage

Question

I'm new to the IMAP protocol and Zend_Mail_Storage and I'm writing a small php script for a cron job that should regularly poll an IMAP account and check for new messages, and send an e-mail if new messages have arrived.

As you can imagine, I want to only poll the IMAP account for relevant messages, and I only want to send a new e-mail if new messages have arrived since the last polled new message. So I thought of keeping track of the last unread message I polled with some unique identifier for a message.

But I'm a bit uncertain about whether the methods I want to utilize for this do what I expect them to do though.

So my question is:

• Does the iterator position of Zend_Mail_Storage_Imap actually resemble some IMAP unique identifier for messages, or is it simply only and internal position of Zend_Mail_Storage_Abstract? For instance, if I tell it to seek() to message 5 (which I stored from an earlier session) will it indeed seek to the appropriate message on the IMAP server, even if for instance messages have been deleted since last session?

If you could shed some light on this matter, I'ld appreciate it. Thanks in advance.