When we started with BladeWP we made the choice to only focus on WordPress hosting. Hosting other things would be possible but when you want to be good at something you have to focus on that.
Most of our customers use Google Suite and Office 365. Another part of our customers use the email hosting they already had when they migrated to BladeWP, most of the times that is still with their domain registrar.
If you change to another email provider you have to think about saving your emails and/or moving the emails over to the new provider. Not all email providers provide such service so in most cases you have to do it yourself.