If you find the Mailock button has disappeared from the ribbon the most likely reason is that Outlook has removed it.
Outlook monitors its add-ins and deactivates any it believes is causing any issues. Usually there is nothing wrong with the Mailock Add-in, other than Outlook believes it is taking too long to start.
To get the button back, the first thing to do is to check how Outlook has deactivated the add-in:
In Outlook, click on 'File' at the top left.
Next, choose 'Options'.
Followed by 'Add-ins'.
This takes you to the list of all add-ins in Outlook. Look for one called 'Beyond Encryption' in either:
Once you've found it, follow the corresponding steps below.
Inactive Application Add-ins
This can occur if the add-in has caused an error, but not one that caused Outlook to close, or if Outlook thinks the add-in is taking too long to start.
Disabled Application Add-ins
This can occur if the add-in has caused Outlook to close unexpectedly.