EDIT: HN's contact email is working fine; the evidence presented was known to be invalid before it was posted and used in bad faith to bait the conversation.
It worked fine when I emailed them yesterday using a non-Gmail email client and server. You’re suggesting that all email for YCombinator is down (or, worse, some/all of Google Apps) so that seems worth proving out. I checked and there aren’t any posts today about Gmail or Gapps being down. Diagnostic superpowers, activate!
Are you getting a bounce/timeout from a real email client through a real SMTP server? I know some mail servers I used to operate would reject your telnet test as shown, so I’m not really surprised it failed at a Google SMTP endpoint.
Are you attempting to email them using Gmail, using a third-party commercial service, via a cloud/datacenter-hosted personal SMTP server, or a home internet connection SMTP server?
If the SMTP server is under your control, is TLS correctly configured on it to modern standards? Do your server’s A/PTR records match the hostname it’s configured to use?