With 2 Outgoing Mail Servers, how can a plugin pick one over the other to send email

[KC Integrations]

Hi,

I am writing a plugin that requires emails to be sent to a list of external emails (like a mail-out service). These external emails do not belong to users of Confluence.

The requirement is to make the emails sent to these external email addresses look like they come from a support account, not from the default confluence account that our confluence users currently see.

For this, I have set up a second outgoing Mail Server with a new and different FROM email.

My problem is, that I have no way of picking this Mail Server from the list of mail servers when adding mail to the mail TaskManager. Using the prescribe method: https://confluence.atlassian.com/doc/preparing-for-confluence-7-0-950280675.html#PreparingforConfluence7.0-Atlassian-mailupgrade 

I'm sure this must be possible, either by specifying another queue name other than "mail" or somehow setting which MailServer to send the email on. This seems like such a simple option, however I can't find anything on how this might be done.

Does anyone know how this can be done?