Mail on ipad - taking up space

San, did you delete all the Mail or the Mail Accounts? If you deleted the mail in your inbox make sure you also delete all the mail in other folders. Open Mail and click on Mailboxes. Go through each mailbox including Trash, Sent and Junk, etc. and delete anything there. Then go to your Settings > Mail > Sync and change the setting to 2 weeks back. Restart your iPad. You may just have to wait until the Mail App catches up with the new sync. You probably have a lot of old mail with large files attached to them thus your 756MB.

David Pogue wrote a very reliable book on the iPhone and iPad, The Missing Manual, and it recommends what you have already done:

Delete email attachments. Files downloaded with your email take up a lot of space. The solution is to delete the email account (openSettings, then Mail, Contacts, Calendar, then the account name; scroll down and tap Delete Account) — and then add it again. Make sure you know your email passwords before you do this! In the process, you’ll vaporize all the attachment files and message caches that you’ve ever downloaded and opened on your phone. When you add the account back again, those files will still be online, ready to download — but only when you need them. (This trick works for most account types — but not for POP3 accounts.)

The only other thing I can think of is to do a complete reset but this will take time. You would have to do a backup to iTunes first (after you have done the Mail Account, Mail delete). Then do a Reset on your phone, Settings > General > Reset > Erase all content and settings. Then backup from your saved iTunes backup. You should not loose anything if you properly backed up to iTunes first. This generally frees a lot of space stored in various caches, etc. but will take time to perform.