I would like to suggest improvements to the "undo send" feature.

1) At the moment, there are only options: 0, 5, 10 and 20 seconds.
Why not allow users to enter the time period of their choice?
- I would love to delay all my emails by 15 minutes,
- someone might prefer 1 hour,
- etc.

And it's easy to implement.

2) "undo send" should be available in ProtonMail phone apps.

Thanks!