Thanks for the question - you will need to update the email template that you are sending to reflect the correct host.
Customizations > Email Templates > Your Template
Also, please upvote these two related issues, if they would serve to further your use case above.
https://github.com/FusionAuth/fusionauth-issues/issues/88
https://github.com/FusionAuth/fusionauth-issues/issues/457
Thanks,
Josh