Can I UNSEND mail in Google mail?
No, but you can set up a timed delay.
How to Set up “Unsend an Email” feature
Click the Gear
Scroll to Settings
Choose the General Tab
Scroll to Undo Send
Choose how many seconds you wish to allow yourself to unsend an email (up to 30 seconds)
Save Changes
One last thing...you won’t see the message to UNSEND if you haven’t dealt with the following message on the bottom left of your mail screen. Click to ENABLE Google desktop mail alerts.See pic below.
Once you ENABLE this, you will be able to see the UNSEND link. The link opens behind this message. 