Exchange 2013 - Cert Issue

Have Exchange 2013 server with what appears to be issue with expired cert.  Cannot receive any inbound emails.  We put in a new cert set to expire in 2018 into Exchange, went through the entire process of importing it, then through the Admin Center completing the process.  It shows as a valid cert and has since June 2015.  Old cert expired on 10/20/2015 but never gave it any thought because we had the new cert in place.  AS of this morning, no inbound emails from outside senders.  Current cert says Date Invalid which is correct.  However, new cert shows Valid with expiration date of 6/28/2018.  Services for the new cert show IMAP, Pop, IIS, SMTP, just like the old cert does.  How come my server is not using the newest cert that expires in 6/28/2018?  What happens if I delete the old expired cert?  Will Exchange automatically begin using the correct cert?
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HariomExchange ExpertsCommented:
First test that the SSL certificate is working you can browse to the Outlook Web App URL for that server and see whether you receive an invalid certificate warning from your web browser.

if no warning then everything is fine , if getting error than you can deleted the old certificate and re enable new exchange certificate using following article.

It might be possible that there are 2 certificate (Self Signed + CA Signed) is assign to SMTP service

You can verify the same as per following article and do it accordingly.

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