Issue Email security SSL issues

[Cyberchute]

We started seeing reports of email error messages from customers:

Cannot Verify
Server Identity
The identity of
"---"
cannot be verified.

We are using Let's Encrypt for the server certificates but last week the errors began to appear as something expired. The server management (not to be named) has escalated the issue but the solutions provided have proven useless.

• Changed settings for smtp/imap/pop3 -- No change
• Reinstated the SSL certificate -- No change
• Turned off SSL on accounts on phone and computer (Outlook) -- No change

Getting desperate.... Monday I expect to be flooded with angry customers who can't use their phones and can't send email. Some messages are being downloaded among a flurry of error messages. Email issues are our #1 cause of customer attrition ahead of death, retirement and businesses closing.

This has dragged on for several days. It is common for support issues to go on for days with this company, even before COVID. I am also open to suggestions for a new server manager.