[12.x] Make it more clear what is happening with email RFC validation

[tanerkay]

As of a commit since 12.x, the email validation docs could be seen as misleading/confusing.

The email validation does not validate against RFC 5322, but also allows other RFCs. This is important, as other RFCs allow emails that are not compatible with several (most?) major email platforms.

Also, the strict validation mentions "rejecting trailing periods or multiple consecutive periods", which I think is an oversimplification.

I don't see a way in the upstream egulias/EmailValidator to selectively validate against certain RFCs.

As the list of RFCs is subject to change, I propose changing the docs to mention "supported RFCs", with a link to the list. The link might be deemed superfluous as the package itself is linked to earlier in this docs section.

Alternative approach would be to delegate to the egulias/EmailValidator docs for the rfc and strict rule styles.

Related topics:

• 5.8 Email validation changes ideas#1555
• Email validation treats emails as valid even if they are not framework#27875