indeed, once the email leaves our servers we have no way to adjust to the recipients timezone
there was some previous discussion on this: Discourse local dates need better presentation in emails
switching to UTC was an improvement over not showing any timezone, or a very verbose situation where we might show 3 timezones for every date… but there still hasn’t been a follow-up to utilize a site/user timezone.
Even if it’s a few timezones away, many people can probably take a better guess when starting from a specific timezone rather than UTC.