Google and Yahoo are hurrying to optimize their e-mail clients for a mobile device that has elbowed aside the BlackBerry in the number of e-mail users, according to some statistics: the iPad.

Google first introduced a new version of Gmail for mobile for iOS and Android in April, including a redesign of the underlying code. Now it has rolled out its so-called Stacked Cards Interface on the iPad that lets users select and manage multiple conversations.

Also, the week Yahoo introduced its own an iPad e-mail offering: HTML5 mobile Web mail. Among its features is local caching capabilities to access and search messages even without an Internet connection, full search capabilities and a dual-pane view.

Catching Up

The iPad had its debut only this year, but it has quickly attracted a robust following. New JangoMail statistics show that out of 17.3 million marketing e-mails sent by JangoMail customers last month 640,000 were opened via the iPhone, 77,000 via the iPad, and 11,000 via the BlackBerry.

However, the desktop still reigns, it noted: 10 million e-mails were opened via Internet Explorer, 3.1 million via Safari, and 2.9 million via Firefox. 163,000 were opened via Outlook.