Validating common email typos without MX/network lookup, using public suffix gem

[eliotsykes]

I'm researching preventing common TLD and public suffix typos like "mailbox@gmail.cpm", whilst avoiding an MX lookup for performance reasons.

One proposed solution is to check the address domain against the public suffix database using strict validation:

PublicSuffix.valid?("gmail.cpm", default_rule: nil)
# => false

PublicSuffix.valid?("gmail.com", default_rule: nil)
# => true

Do you think this is something that would be a worthwhile addition to the email_address gem, perhaps as a host_validation: :public_suffix option?

[eliotsykes]

Closing this issue as I've learned more about the public suffix database, and tried it against some real emails, its validation throws up some false negatives.

For example "@gov.bm" and "@sa.gov.au" are valid email domains but the public suffix db will flag them as invalid.

Possibly the public suffix db could be used only as a positive signal:

• If an email domain passes public suffix validation, treat is as valid
• If an email domain fails public suffix validation, only then perform an MX lookup (minimizes network trips, consider caching the result)