I currently run a Plesk VPS, with 2 Domains hosted within.
Some time ago, I had installed the 'Let's Encrypt' SSL Certificate onto my Plesk VPS. Both domains, successfully displayed the 'https' prefix within the domain and I was able to use the emails with no problems, within Outlook 2016.
Recently, I have started to receive the following 'Internet Security Warning' whenever I try to add new emails into Outlook 2016.
I have spoken with Plesk, my hosting company. Microsoft and Let's Encrypt, with all parties stating differing errors, explaining I need to speak with the other party.
Is anyone able to point me in a possible direction, as to resolve this issue?