Hello @samlinck,
First of all, you’re welcome for the quick response we strive for.
About the follow-up question, you inquired to know if it is possible to use one of those email addresses inside a custom plugin.
Yes, you can add as many as you want in the FluentSMTP and then use any one of them through your WordPress and that will automatically be used by FluentSTMP.
Regarding the library you referred to, using it may cause an issue since WordPress supports a single SMTP Plugin or Mailer.
I hope this clarifies things. If you have more questions or need further assistance, don’t hesitate to reach out.