Something of an experiment here. 

Proton Technologies in Switzerland provide extremely high security comms, VPN's and email.  We use Proton for all our data protection customers, and if we can get our DNN portal to use the outward SMTP option we have a unified Intranet with the rest of the operations.

However, when installing their Bridge application  that creates a black box service for Proton on a VPS server, DNN errors back " Certificate is invalid according to the validation protocol". 

The basic DNN configuration is limited to what's normally needed, anyone any suggestions for how we might get around this?

thanks