[blueflow]

Doesn't require, but comfortably allows you to do.

[unilynx]

Agreed.

But this is SMTP, I have no doubt there are gateways out there that will reencode the mail and put the dot back in the wrong place, eg in the name of wrapping all URLs behind a phishing-warning-page

[opello]

I think the point here is that any subsequent implementation handling the message may well not be susceptible to the problem thus avoiding the erroneous behavior.

[int_19h]

It can handle it fine in that sense, but still unquote it before sending it over to the next node. Which might have the bug.