async function getLastEmail() {
    const mailgunCreateMessageStub = mockManager.getMailgunCreateMessageStub();
    assert.ok(mailgunCreateMessageStub);
    sinon.assert.called(mailgunCreateMessageStub);

    const messageData = mailgunCreateMessageStub.lastCall.lastArg;
    let html = messageData.html;
    let plaintext = messageData.text;
    const recipientVariables = JSON.parse(messageData['recipient-variables']);
    const recipientData = recipientVariables[Object.keys(recipientVariables)[0]];

    for (const [key, value] of Object.entries(recipientData)) {
        html = html.replace(new RegExp(`%recipient.${key}%`, 'g'), value);
        plaintext = plaintext.replace(new RegExp(`%recipient.${key}%`, 'g'), value);
    }

    return {
        emailModel: lastEmailModel,
        ...messageData,
        html,
        plaintext,
        recipientData
    };
}
Returns the last email that was sent via the stub, with all recipient variables replaced
@returns {Promise<SendEmail>}