- Allow sending larger attachments (Windows; Android)
- Allows to send higher quality photos (mainly refers to the camera to take photos, Android)
- Read the image in the clipboard when pressing Ctrl + V (Windows)
- Allow self-starting, and automatically minimize to the tray when starting (Windows)
- Allow custom installation path (installer, Windows)
- Allow custom user data path (installer; portable version, Windows)
- The sent messages are synchronized in real time across multiple devices. (Windows; Android)
- It is forbidden to download attachments automatically (Windows; Android). The specific manifestation is that the message bubble only displays the icon; the file name; the size and the text message. The download will only start after the user clicks the icon.
this kind of feature is requested quite often, hope it is implemented sometime 
but the current efforts are about email compatibility which is a huge improvement! (mailing lists, see original html emails, etc)
Email compatibility: done. 
Now it’s time! 
most of the above is done, so closing stale topic.
as a general note, as also mentioned in the category description, it is better to create dedicated topic per feature proposals