@doenietzomoeilijk my stance is that there are four states of email validation. Not two: valid/invalid. But four:
1 pending validation.
2 confirmed valid in the past.
3 probably invalid.
4 confirmed invalid.
Most apps will only need 1&2. 3&4 are when you start getting bounces or errors. 2 in practice means: (confirmation)email was read (proven by eg clicking a link)
@doenietzomoeilijk and 'valid' has an expiration. An address may be valid today, but invalid tomorrow. E.g when a person leaves a company, school, provider.
Which, again, is easily solved by not regex-validating, but just sending the mail: as long as it arrives, it is valid. As long as it is read, that's confirmed valid.
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