alter email address in DB to render it un-deliverable

Question

I need to alter email addresses of users to render them undeliverable (not ever a real address), however it needs to be reversible so that the original is visible or at least retrievable (without storing it elsewhere).

For example john@example.com -> NONAME_john@exampleNOTHING.com might work as it can be changed back. However, the problem is that I cannot KNOW that the above-resulting address is not a real email address. Maybe there is a real address out there called NONAME_john@exampleNOTHING.com.

The requirements are that the address needs to be valid (in terms of having '@' and '.com' etc) but won't send.

Maybe my requirements are a contradiction and hence not possible? Does anyone know?

Answer 1

Your requirements are kind of a contradiction. The only way to make an addres unworkable is to render it practically invalid.

Note that "invalid" can mean at least three things;

1. it doesn't parse as an e-mail address (e.g. replace @ by ⓐ)
2. the user name is invalid at that domain
3. the domain name is invalid

The point is that for 2 and 3 there is no easy way to know for sure if that is the case.

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What you also could do is obfuscate the e-mail addres by applying a reversable transformation, like e.g. base64 encoding it. This falls under category 1 above.

For example in Python 3:

In [1]: import base64 

In [2]: base64.b64encode('john@example.com'.encode('utf-8')) 
Out[2]: b'am9obkBleGFtcGxlLmNvbQ=='

In [3]: base64.b64decode(b'am9obkBleGFtcGxlLmNvbQ==').decode('utf-8') 
Out[3]: 'john@example.com'