[Gathering6678]

I suppose it would be trivial to simply block or severely throttle high-volume SMTP traffic?

[userbinator]

Additionally, this will make it look like you're a spammer.

[stackskipton]

You could block SMTP on almost all end user networks with no one noticing. 99.9+% of email client submission is HTTPS.

[bauruine]

I doubt it's that much but with the same logic you could also ban HN, SSH and basically any protocol thats not https "with no one noticing" because 99.9+% doesnt use it.

[ranger_danger]

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