Outlook 2016 - security certificate issue when opening outlook
I have Office365 locally installed on a PC with the email account setup as IMAP. All was working ok but now have a few issues:
1) When opening Outlook frequently (not always) getting a send/receive error - usually a reboot will correct
2) Yesterday - started getting the following message: "Internet Security Warning" - The server you are connected to is using a security certificate that cannot be verified..... do you want to continue using this server.
I have two different email accounts setup in Outlook (one goes through Yahoo servers and the other through Total Server Solutions (previously Hands On Webhosting) - both accounts are setup as IMAP.
Better to test + know, than guess.
Provide the hostname of the IMAP server you're connecting to for testing.
If you must do this yourself, what you're looking for is if the IMAP instance has a fixed IP or an IP pool.
What you describe sounds like an IP pool, where one or more IPs have some config which is incorrectly serving your cert.