IMAP SSL In exchange 2013 with Nat address

Hello Guys,

Please help me out, i am really stuck with IMAP SSL configuration.

I have external interface which is nat ing all the traffic which comes on port 993 to the internal Exchange server and i have already done this configuration on the exchange server.

Start-ServiceMSExchangeIMAP4; Start-ServiceMSExchangeIMAP4BE

INFO: I use the wild card certificate for all other email services and it just works fine except when i try to assign the IMAP Services to the Wildcard certificate and i get this error mentioned below

This certificate with thumbprint and subject ‘*.domain.com’ cannot used for IMAP SSL/TLS connections because the subject is not a Fully Qualified Domain Name (FQDN). Use command Set-IMAPSettings to set X509CertificateName to the FQDN of the service.

and when run the Set-ImapSettings command , I gets this error messages below.

Set-ImapSettings -ExternalConnectionSettings “mail.domain.com:993:SSL”,”mail.domain.com::143:TLS" -X509CertificateName Mail_Wildcard_Cert

The certificate with the subject ‘mail_Wildcard_cert’ can't be used for SSL or TLS connections because the subject

isn't a valid fully qualified domain name (FQDN).

Please help me find my mistake, 

thank you for all the help…