We use Opera DDS secure email. Every specialty office we refer to uses their own secure email system so you end up with a series of user names for each one.
We use Softdent Cloud. We use Protected Trust (PT) encrypted email, $15/month. Yes...it would be another website to open when you need to use it.
Do you have outlook 365? You can add on an additional service to your outlook mailboxes that encrypts emails so they are secure and HIPAA compliant. The additional service costs around $2/month per mailbox set up. Your IT should be able to take care of this. We just enabled this service 2 weeks ago and haven't gotten a single push back from our referring doctors.