How can I auto-pupulate the To and From fields when sending an email?

What is the simplest way to auto-populate the to/from fields on the mailgun page so the user only needs to type in the subject line and text body fields when sending an email?

To clarify, because an email would only be sent to me, the to field would just be my email.

The from field would auto-populate with the email the user registered when signing up for app.
1 person has
this question