Notice there is not a little arrow inside that dropdown and no option to Add New = Not a list you get to maintain.
These are Functional, not notational. The setting for Email will operate the Send Later function in the customer's transactions that you create. The "Mail" function used to be linked to a Mailing Service provided by Intuit.
If you want to Notate something, use the First tab = Address Info, seen when you Edit Customer. FAX is right here. Example:
I can provide you with some information about adding fax for the delivery method in QuickBooks Desktop.
Adding fax for the delivery method in the payments settings is currently unavailable in QuickBooks Desktop.
I can definitely see how this feature would be useful. As a team with a massive road-map, we have to pick new features based on the value they’ll add to the most users possible. I recommend sending this request straight to our product engineers through feedback.
Click Help at the top.
Select Send Feedback Online.
Then click Product Suggestion.
The Product Development Team is constantly working to improve QuickBooks and make it even better for you as the customer. I'll share your feedback with them to let them know about the changes you'd like to see made.
As always, if you need help with QuickBooks you can call our dedicated team who will be happy to assist you. Our contact details can be found here along with our opening hours: