Host validation for 'sub' does not allow domains containing hyphen

[ngdio]

The host validation introduced in 871d67d does not allow domains that contain hyphens to pass through the check, although they should be perfectly valid domains.

Working: test@testingthis.org

Not working: test@testing-this.org

This is also causing the issue described in home-assistant/core#48766.

[wshuman3]

I believe the PR that introduced this was #92 not #91

[wshuman3]

#96 should resolve this issue