What are the rules/proper etiquette for emailing an Orthodox Jew after sundown on a Friday?

Is it simply not ok to send them an email late on a Friday, and one instead should wait until Saturday night? It’s understood (by the sender) that there’s no chance they’ll read it until Saturday night at the earliest, but does someone need to hold off on sending an email just because the recipient (or even just someone copied on a trail) is Orthodox?

And does it perhaps depend if the sender is Jewish or not? Is it ok for a non-Jew (as it’s fine that they are still working) to send an email to an Orthodox Jew Friday night, but perhaps not ok for a non-Orthodox Jew to do so (as, even if they aren’t Orthodox, they should still ‘know better’ than to send it)?

Thank you.