the module picks up the wrong domain

The module using a very narrow logic to pick the working domain from Mailgun domains, now it picks the closest domain to the domain used with the sender email. I think the module needs to give the site admin a configuration to decide which domain to use to send out the message, or to check the current site domain and match that with mailgun active domains. in our case we have multiple sub-domain domains, a sub-domain for every site dev/staging/production. and we use a sender email that is only matching one of the sub-domains.