I thought I had suggested this previously, but can't find my suggestion in this ofrum.
I'd like an option to add the *recipient(s)* of a messages to an addressbook. Even better, I would like a global setting to create an entry in a specified addressbook for any (new) recipient of a message I send.
There's a right-click option to add the sender to an addressbook, but no option to add the recipient.
There are workarounds, of course, but they are inconvenient.
I receive many messages from people/addresses mthat i am unlikely ever to want to contact again. But if I send a message to an address (the first time I do so, it will typically be by using "reply"), there is a good chance that I will want to send a message to that person/address again at soem unknown time in the future -- and therefore will want to be able to find them in my addressbook.
In the absence of this feature, i often have to perform searches of my mail archives of copy-self folder(s) to find the address of someone who I have corresponded with in the past.