[Skywing]

How does the undo send work? Does it store the email on your server for X seconds before dispatching through gmail?

[DarwinMailApp]

Nope!

It doesn't send the email until after 0 - 30 seconds, so you have a chance to undo it :)

[leesalminen]

So, if I were to close the app at second 17, the email wouldn’t get sent?

[DarwinMailApp]

That is correct. However, would you think again if a little pop-up reminder told you just before you exited the app? To be fair though, I keep my email tab opened all day. I never close it!