Can't send Welcome Email after Public IP change

[TCF]

I recently put our PBX system on its own network with its own cable modem. Since doing so I'm unable to send Welcome emails. I get the error message An exception occurred Error: The remote certificate is invalid according to the validation procedure. I can send email using telnet so I know it isn't a firewall issue. I also get a message inside my SMTP Server (I am using BEST SMTP Server as the relay to office365) that my IP Address is dynamic and that I need to change it to a static IP, but it is a static IP. Any help is appreciated.

 

[TCF]

I bypassed our local smtp server and sent it directly to smtp.office365.com which is working fine.