I hard coded this. You want to edit line 74 in mailgun.js.
The original file looks like this:
messageData = {
to: Object.keys(recipientData),
from: message.from,
'h:Reply-To': message.replyTo || message.reply_to,
subject: messageContent.subject,
html: messageContent.html,
text: messageContent.plaintext,
'recipient-variables': recipientData
};
You want it to look like this
messageData = {
to: Object.keys(recipientData),
from: `"CUSTOM-FROM-NAME" <YOUREMAIL@DOMAIN.COM>`,
'h:Reply-To': message.replyTo || message.reply_to,
subject: messageContent.subject,
html: messageContent.html,
text: messageContent.plaintext,
'recipient-variables': recipientData
};