I deleted my Inbox by mistake. Have over 5000 mails in Deleted folder. If I select the 'All' checkbox I don't get the option to Move to Inbox. But if I select a group of mails, say 30, I do. Is there a way to bulk move all mails back to Inbox?
You should try to connect with an email client (Outlook 2016, Thunderbird) over IMAP. When your Mails are synchronized you can move all from the Deleted Mails to your INBOX again.
Be aware that to move the mails will take a few moments !
Unfortunately, you can't choose more than a page at a time to act on with the web interface. (See this answer from answers.microsoft.com.)
To select all of the messages on a page, click the checkbox at the top of the list (next to the "View" menu, which defaults to "All").
Open the "Move to" menu at the top of the page, and select "Inbox".