In notify-mailer, policy.ValidEmail sometimes rejects valid e-mail addresses

[jprenken]

Boulder checks the Public Suffix List (among other things) to disallow registering with an invalid e-mail address. However, the PSL changes from time to time (and/or the check was once more permissive). The policy.ValidEmail check keeps notify-mailer from being able to e-mail certain existing subscribers.

Most of the affected e-mail addresses are invalid, but not all: a few ICANN TLDs in the Public Suffix List do have MX records, and are apparently actively used for e-mail. notify-mailer will skip them:

skipping "redacted": contact e-mail "redacted" has invalid domain : Domain name is an ICANN TLD

[aarongable]

Update: we already check the public suffix list when ingesting email addresses, so we should stop checking it when sending mail (we expect the undeliverable rate to remain low, and this will prevent false-negatives).