Talk to them...

"We currently use Gmail for our email that's correct.

We always recommend users using pgp as basically any other form of emailing shouldn't be considered safe.
We are working on our own self-hosted email platform utilizing our STBOOT ( https://mullvad.net/en/blog/tag/system-transparency ).
It's currently in internal testing and being audited, so hopefully it should be finalized and released this year."