As it says in the title, just some important and relatively minor improvements to Mail (both web and desktop app), in no particular order.

Where messages are grouped as conversation, the ability to permanently delete single messages, whether sent or received.

In message list view, instead of the page indication - e.g., '1/3' - the numbers of the messages displayed currently, e.g., '51-100/245'.

Also in message list view, instead of the day/date of messages or conversations, date and time - e.g., '24/06/10 14:56' - except for 'Today' just time additionally.

Perhaps the facility of selecting a number of messages to be printed to a single PDF, as mentioned elsewhere also, plus perhaps option to print selected messages each to separate PDF.

Proton Sentinel to open in a new browser tab for the Mail web app.

I'm happy to note that an essential 'Reply To' facility that should have been available in Mail from the beginning has already been requested and IIRC is already being reviewed.

Messages that come from the user's aliases should be able to be replied to from that alias.

I think that's all for now. I am well aware that this list consists of more than one single suggestion, but think it makes sense to list these together as they are all small or fairly small improvements.