It should for Gmail. If you read the article about BIS 2.6 it listed the updates.
If not here are the updates:
* IMAP integration of Gmail® webmail accounts. This integration protocol introduces the following benefits: |
* Elimination of duplicate Gmail messages appearing as received email messages; and
* One-way synchronization of read status, sent items, and deleted items.
* GMail accounts which were integrated before BIS 2.6 will require deletion from the BIS and setting that account back up on the new BIS (which basically provides for the new service book to be pushed to your device).