Reply & Archive — Inbox Zero user? Now you can Reply & Archive a conversation in one go. Go to Preferences > General > Conversation View > Reply & Archive
Bulk Snooze — Select multiple mails from the list and snooze them.
New setting to show full signature only on your first mail in a conversation and just your First Name on the subsequent ones. Go to Preferences > Email Accounts > Signature > Show signature on
Windows
Send bigger attachments. Go to Settings > Exchange/IMAP Email accounts > Set Max attachment size. For other accounts, it just works.
In compose the From Address automatically corrects itself based on recipients.
Signature settings got formatting options. Also an option to upload html.
Android
New setting to make you stay in All Inboxes, when you tap on new mail notifications. Go to Settings > General > All Inboxes > Stay in All Inboxes