If so, it's not that unusual that it wouldn't be supported. The local-part used to be constrained to ascii only. RFC6530 (SMTPUTF8) added UTF-8 support, but it's optional. Google only started supporting it in 2014, for example: https://googleblog.blogspot.com/2014/08/a-first-step-toward-... Microsoft has support in some places, but not others, etc.
The article notes that fixing it in the python client doesn't fix the upstream lack of support on mailchimp's back end.
This just seems to be a case of high expectations. Support of utf8 local-part is spotty across lots of providers and software.
These users? You couldn't even email them from Outlook until just last year, 2016! How many users in the world would have accepted having an email account that no one using Exchange servers could handle? That cuts you (the user) off from hundreds of millions of people on corporate networks.
Arguably an advantage.
Fastmail, which is pretty popular here, only allows a-z0-9_ in usernames. I don't see a "250 SMTPUTF8" reply when I connect to their server and EHLO. So, it's likely they don't support it either.
However, they don't appear to support it for firstname.lastname@example.org. Either for sign up, or for live delivery. http://imgur.com/a/Otf4f (see both images)
Try sending to 안녕@mydomain from a gmail account...it looks like they may not be supporting SMTPUTF8 correctly. Which could result in sending-to-yourself working, but not from an outside source.
For some reason this person calls an email address an email.
In Poland, for example, it's common to use the word "e-mail" when one means "e-mail address", e.g. "give me your e-mail".
Perhaps other readers will find that useful to figure out the intended message.
Language nitpick: that should be the other way around, for meaning roughly instead of in this expression. I guess this might be going the way of comprised of and the like (once considered a clear error, but now so widespread that it's considered pedantic to reject it).
Doctorow was on over 3,000 lists. Unsubscribing was a lot of work. The cynic in me says that's how MailChimp wants it.
Although MailChimp can process UTF-8 characters in most parts of our application, we cannot process UTF-8 characters in your subscribers' email address prefixes. We do accept Internationalized Domain Name (IDN) servers, so it’s alright to have UTF-8 characters in the domain name.
For example, we’ll block direcciónelectrónica@domain.com because the international characters are in the prefix, but we'll allow an address like test@ñoñó1234.com, where the characters are in the domain."