Remove certain functionalities from DomainAddress

[say-yawn]

About this Issue

From #812, which closes #808, we added the following functionalities to DomainAddress:

• create DomainAddress impromptu (e.g. alias generated at first emailed)
  • E.g., When I'm at the donut shop and they ask for an email address to send my receipt, I want to make up "[email protected]" and have it automatically forward to my real address.
• create 'DomainAddress' randomly--like RelayAddress
  • E.g., When I click an article on wired.com and it prompts me for an email address, I want (my Relay add-on to help me) to make a random address at my domain, like "[email protected]".
• create DomainAddress with a specific alias
  • E.g., When I sign up for an account at stackoverflow.com, I want (my Relay add-on to help me) to make a specific address at my domain, like "[email protected]"

Currently we do not know if/how the random alias generation will be used on DomainAddress and we should either remove or fix the FIXME here and here one we come to the decision.

Acceptance Criteria

• Finish technical document on DomainAddress
• Get input from Product
• Get input from Design
• Make decision to support or remove random alias creation functionality

[say-yawn]

Relevant comments 1, 2, 3, 4, and 5

[groovecoder]

As I outlined specific example user stories for the 3 different ways users could interact with domain aliases, it occurred to me ...

ALL of the use-cases are addressed by the "impromptu" use-case that we already have in the code.

• "random domain address" - someone can make up a random localpart already without Relay (add-on) helping them
• "specific domain address" - someone can make up a specific localpart already without Relay (add-on) helping them

So, I propose we only include the "impromptu" domain address use-case in our initial scope.

It will cut down work (we won't have to design & build add-on UI for the "random" and "specific" domain addresses), and we can always iterate later if we have user feedback (e.g., AMO reviews) asking us to streamline the "random" and "specific" domain address use-cases.