Can't send encrypted email on Galaxy S8

[Android Central Question]

I've setup the default email app on my S8 for Exchange ActiveSync and everything works fine except I cannot send encrypted emails to recipients. The error message I'm receiving is 'invalid certificate'. Is the email app not capable of getting the recipients .pfx certificate that is published to GAL on our exchange server? I've also tried having a recipient send me a digitally signed email and then adding them to contacts before trying to send them an encrypted email and I get the same error message about the certificate being invalid. I am able read encrypted emails since I have my root and personal certificate installed on the phone. I have tried many things to get this working but so far no luck. Any ideas would be appreciated!

Thanks!