If the macro is being launched from the Finder, this can be done largely by taking advantage of built-in Copy and Paste capabilities. The macro shown
- copies the selected files in the Finder;
- has AppleScript activate Mail and make a new message;
- uses Keyboard Maestro to move to the body of the email and paste the files;
- Keyboard Maestro then moves the cursor to the beginning of the message body in case you need to add/change the message;
- finally, Keyboard Maestro deletes from the clipboard the files that were copied.
Here's the AppleScript which needs some editing for use with your email information and recipient information.
tell application "Mail"
activate
set theOutMessage to make new outgoing message with properties {visible:true}
tell theOutMessage
make new to recipient at end of to recipients with properties {address:"first@mail.com"}
set sender to "Name Surname <name.surname@mail.com>"
set subject to "Message Subject" --optional
set content to "Message Text" --optional
end tell
end tell