By default, Outlook will automatically disable any plug-in that experiences a delay during startup. Because the SendSafely plug-in checks for updates when Outlook is started, this sometimes results in Outlook disabling the SendSafely Plug-in.
There are two ways to fix this issue:
Option 1 - Choose "Always Enable" from the "Slow and Disabled Plugins" list
In Outlook, check the "File" menu and press the "Slow and Disabled Add-Ins" button. From there, see if SendSafely for Outlook is listed. If so there should be a button that says "Always enable this add-in". More information on how to do this is also available on the Microsoft Office website: https://blogs.office.com/2012/10/08/take-control-of-your-outlook-2013-add-ins/
Option 2 - Add SendSafely to Outlook's "Do not Disable" List
SendSafely has developed a registry file that will add our plug-in to Outlook's "Do not Disable" list of plug-ins.This file will add the appropriate entries to the Windows system so that Outlook will no longer automatically disable the SendSafely plugin.
Download and run the attached .reg file (choose YES when prompted), and then restart Outlook.