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As far as I understand from your thread, you need use your custom email address service provider to get "Notification" or "Autoresponder".
To do that, you need to follow the steps from the below:
1) The first thing you do is go to your current "Notification".
2) Then, click to "Reply-To and Recipient Settings".
3) In the "Provide Sender and Recipient Details", click to "Sender Email", then hit "Add a Sender Email".
4) On the following window, enter your email address and the verification code will be sent to you again. When you get the code, copy and paste it on the same "SMTP Account Wizard" window which is shown below:
If you still don't get the verification code, I suggest you to check your junk, spam, etc boxes from your email.