GMail has a fantastic web interface, but somethings are just much easier with a desktop application. Google don’t offer any desktop Gmail client, although they do offer support for any e-mail client through POP, there is no way to see GMail’s Conversation View, no way to filter with or apply lables or the excellent search.
The best feature of Mailplane is the ability to drag and drop attachments directly into the composing message window. This effectively reduces a four-step process1 to a simple drag and drop action.
It can also resize and compress images you attach to be more web-friend in size. The amount of compression and size is changeable, although the default setting is quite well balanced. Mailplane can also integrate with iPhoto, although as I don’t use iPhoto I can’t comment on this feature. The getting started video shows you how to send a photo directly from iPhoto.
Mailplane also has a very slick feature where you can send a screenshot just by selecting the area of the screen you want to send, and then Mailplane resizes, compresses and uploads the attachment for you. This is an incredibly useful feature, that apps like Adium also need to have.
Mailplane supports you having more than one Gmail account. You can flip between them in the account side bar, although unfortunately Mailplane has to load up the Gmail web interface every time for each account rather than storing each session like tabs in a browser, which limits the usability of this feature.
Hopefully the limitations of the accounts feature will be solved in future releases.
Mailplane has support for Growl notifications, and opens the message in a window when you click on the Growl bubble. Neat.
Mailplane also includes Mail.app style keyboard shortcuts and directly mailing anything printable with “Mail PDF with Mailplane” option in the OS X Print window. Overall Mailplane is features very nice additions to GMail that Google should already have2 We’ll have to wait for the final pricing of Mailplane to see if it gives good value for money, but the beta is looking very promising.