someone@arstechnіca.com, is it really from someone at Ars? Most definitely not—the domain in that email address is not the same arstechnica.com that you know. The 'і' character in there is from the Cyrillic script and not the Latin alphabet.
This isn't a novel problem, either. Up until a few years ago (but not anymore), modern browsers did not make any visible distinction when domains containing mixed character sets were typed into the address bar.
And it turns out Microsoft Outlook is no exception, but the problem just got worse: emails originating from a lookalike domain in Outlook would show the contact card of a real person, who is actually registered to the legitimate domain, not the lookalike address.
This week, infosec professional and pentester DobbyWanKenobi demonstrated how they were able to trick the Address Book component of Microsoft Office to display a real person's contact info for a spoofed sender email address by using IDNs.