Another friendly reminder:
Mastodon is awesome, but mastodon isn't an appropriate tool if you want private communications. DMs aren't actually private, they can be seen by instance admins and maybe by other people, it isn't at all secure.
Mastodon and GNU social aren't made for private conversations, if you want to have a private conversation there are many tools that are appropriate for that.
I suggest Tox, but Cryptocat and XMPP with OTR are also good. There are others but I have used those