Mailbox pooling pre-emptive criteria is set forth for use in an adaptive polling system for synchronizing data between a mail server and a mobile communication device. The polling engine stores an indication of the number of messages in the mailbox, the total mailbox size (i.e. the used storage size in bytes), and the last message ID from the last poll. In the next poll, the polling engine retrieves this information from the mailbox and checks against the values stored from the last poll. If the information is the same, then there is no need to compare the message ID list. Whenever either the number of messages in the mailbox or the mailbox size or last message ID has changed, then the full comparison of the message ID list is performed.