Operations on senders from multiple mails

Yes, this is possible with a custom bundle command. I'll see if I can create an example for you when I have some spare time.

I've created an example bundle for you. Unarchive it and create a folder to place it here:

~/Library/Application Support/MailMate/Bundles/

This is highly experimental and the functionality hasn't really been used by anyone else but myself. Nevertheless I think you might like it.

Make sure you have enabled experimental 2.0 features in the General preferences pane (then relaunch if you hadn't).

Now, notice the “Command” menu has an Elektron menu. It has two (badly named) menu items:

Write to Senders
Write to Senders Separately

The first one is what you asked for. Select a number of messages and then create a new message with the senders in the Bcc header (it also checks for any Reply-To addresses). Note that a window is not opened. A draft is simply created in the Drafts folder.

The second one though might be more useful/stylish in some cases. Do the same as above, but note that MailMate now creates a draft for each sender. These drafts can be edited before sending if needed, but they are already personalised with a “Dear xxx,” prefix. This is of course only really useful for standardised messages. You'll have to edit this file in the bundle to change the default text:

~/Library/Application Support/MailMate/Bundles/Elektron.mmBundle/Support/bin/create

Anything could be done in this script including popping up an AppleScript GUI to ask for additional information such a which standard text to use -- or maybe to look up something in a database before creating the message.

Well, it's all very experimental and just intended to give you an idea of what is possible. Let me know if something does not work as expected.