A couple of these are already present in SmarterMail.
1. In Build 9400 (Sept 26, 2025) we released both Undo Send and Schedule Send. The send delay is configurable on a per user basis from the Account settings, on the Email card. The delay times are in seconds: 5, 15, 30, 60. As of now, it's the user's responsibility to set that. I believe the default is 5 seconds. (It can also be disabled.)
2. If you are using a collaboration platform like OnlyOffice or Collabora, and have those integrated with SmarterMail, you do have the ability to open some file types -- those supported by those platforms -- from a message. You simply right click on the attachment and opt to open it in the platform of choice.
#3 is not something currently available, but I'd be happy to add it as a feature request for review. I'd just need a bit more guidance on how you'd want that to work. As of now, compression should occur prior to the attachment being added since pretty much every OS offers some form of compression for files or folders.
Derek Curtis
COO
SmarterTools Inc.
www.smartertools.com