How to generate an app-specific password
1. Compose a new email.
2. Select the Mailbutler feature you want to use eg. Send Later.
3. You will notice that a screen like the one in the image below will pop-up. requesting an App Specific Password. Click on Go to iCloud on the pop-up.
4. You will be redirected to the Apple account website. Log in with your Apple ID and Password.
5. Scroll down to Security. Now under App Specific Passwords, click on Generate Password
6. Next, enter Mailbutler in the box provided ( see image below) and confirm the request by clicking Create. A password will now be created for Mailbutler.
7. You will see the generated app-specific password. Please copy the password and paste it in Apple Mail (See step 1). Finally, click on Login.
You can now enjoy all the feature of Mailbutler with your iCloud account.