Downloading All Mail The user will be able to download a copy of every message from their Gmail account. It will be organized and labeled just as it is on the server. Your filters will still be in effect.
Messages All actions that Gmail provides will be available. Archiving, Trashing, Labeling, 'Deleting Forever,' Marking read & unread, and starring. The full message bodies will be viewable inside the program.
Message Forwarding There have been many programs trying to allow users to forward their old mail into Gmail. GmailerXP will allow the user to do this from a number of formats, 'mbox' and 'pst' being among them.
Starring I personally do not really use this feature, but it will be available in a very similar interface as Gmail.
Filters Users will be able to manage their filters, (Create new, Edit, Delete). Gmail allows for 20 filters, some have said a few more. GmailerXP will give the user two options- either use the filters on Gmail and then when they run out, start making filters locally, Option 2- do away with their online filters completely, and use the local ones only which will intercept all incoming mail and label it and move it accordingly. Local filters may have a few more options than the standard Gmail ones.
Labels The user will be able to manage labels, and bulk delete if they so choose. They can create new labels, edit existing ones, and delete at will.
Contacts The user will be able to manage contacts, and do all operations already provided by Gmail (Adding, Editing, Deleting) as well as import contacts from a number of different formats. The user will also be able to export (backup) their contacts to a number of different formats.
Settings & Preferences All of the user's preferences and settings (Signature, Display Name, and Reply-To Address) will be manageable from within GmailerXP; The user will also be able to change their Gmail password if they so choose.
Sending Messages The user will be able to compose and send new mail. The mail will be saved in their Gmail account under sent messages.
Drafts The user will be able to save drafts locally. Now even though Gmail hasn't come out with this feature yet, GmailerXP will save the 'drafts' locally and they can be used just as if they were on the server.
Multiple Accounts GmailerXP will support multiple accounts, (even though Gmail discourages such behavior ) The user will be able to switch between accounts whilst using the program.
Stats The user's Disk quota and space used information will be visible at all times to the user.
Notification GmailerXP will notify the user of all incoming messages as they arrive with a ballon tooltip that when clicked will open the program and point the user to the message.
Many more features will be coming. Please feel free to post feature requests in the forum!