Drag & Drop or Move To… automatically deletes the copy in the IMAP mailbox
It automatically moves the copy in the IMAP Inbox to the IMAP Trash mailbox. Its complete removal from the server depends on the settings in Mail for that account. (At least in High Sierra, the range of choices for
Erase deleted Messages: includes
Never,
After one day,
After one week,
After one month, and
When quitting Mail.)
