We had an SSL certificate from Let’s Encrypt Authority x3 from September to December this year. It is now expired, and a security alert is popping up in some of our user’s Outlook applications telling them that the certificate has expired. This certificate was not associated with our website. None of our staff remembers signing up for this certificate. But now that it’s expired, some of our users are not able to use their email properly.
How do I get a new certificate to use with Office 365 to bring operations back to normal?
I will try to provide any additional information you ask for.
rg305 - I wish I knew the answers to your questions. None of our staff knows how we got the certificate or how it was installed, or who did it. We just know that the certificate expired and now we’re left in this awkward situation. But to make things even more strange, we’ve used this domain for our email for at least a year so I would assume we’ve had some sort of ssl certificate the whole time… but again, nobody knows who set it up or how.
You have not had a cert for that name the whole time.
There has only been one cert issued to that name:
or to anything ending with that name:
Who made changes to your system on September 10th?
Assuming "that person" is no longer "available" to assist you... You need to figure out where the cert is being used. and maybe how it was inserted.
So you can just repeat the previous method (that worked).
If you can't figure out how, you can just use any method that you are "comfortable with" (from the available ACME clients - for Windows [I presume]).
Well, The weird part is the OP seems to be using Office 365 (Cloud Plan) (Indicated by the MX records), which he should connect directly to office365 servers...
I’m agreeing with @stevenzhu; This cert problem is most likely NOT in AWS.
I would start with a client that has the problem and see where their email client is configured to connect.