If you have incorrectly configured your Outlook 2010 email client, then the server you are connected to may show an error saying that the security certificate cannot be verified. The error may appear as per the screenshot below:
Troubleshooting the Outlook 2010 error: Security Certificate cannot be verified
This error is caused by a mismatch when enabling SSL and your port number in your account settings. Open Account Settings in Outlook and click on the advanced tab. If you need further assistance to open your account settings.
Verify that you are using the correct ports for the incoming and outgoing mail server. If you are going to use the SSL enabled settings you will need to use the correct servers.
You should always use mail.domain.tld for your mail servers.
We recommend using the SSL enable options. If by chance you are in a school or somewhere that may have these ports blocked, you can use the non-ssl settings. The correct ports are below:
Non-SSL incoming POP: 110
Non-SSL incoming IMAP: 143
Non-SSL outgoing SMTP: 587
SSL enabled incoming POP: 995
SSL enabled incoming IMAP: 993
SSL enabled outgoing SMTP: 465
NB : Please ensure you enable Letsencrypt ssl for email via the Letsencrypt plugin via Plesk Interface or cPanel Interfaces.