Looks like this is a problem of your email agent (or any third-party service that you chose to use, which uses outdated non-conforming softwares, that blindly removes the encoding and treats it as if it was ASCII or an old 8-bit charset).
UTF-8 is now **THE** standard of the web, it has won the vast majority of uses and should be supported everywhere, so much that all new web standards (or any revision of them) MUST include its support (this policy has been adopted by the IETF for all new RFCs, and it is part of the essential BCP standard track).
I you have old software that breaks on UTF-8 and still incorrectly retags it blindly as if it was 7-bit ASCII or some ISO8859-* based charset (after silently dropping the encoding that was explicitly encoded in MIME), this software must be updated because it will break with a now vast majority of posts and it has been several decenials that this should have been fixed (even before UTF-8 was standardized when MIME was fixed long before to allow clean identification of charsets and support 8-bit clean transport, using well established transport syntaxes that should have been respected.
I think for example you use some antique software like old versions of MS Outlook or Lotus Notes or other old enterprise software for private use but not maintained at all since long (with no more any form or maintenance: reserve these software only to get access to your own archives, but not to follow new contents posted on the web, and think about adding some correct conversion interface to isolate these archived data and legacy softwares and make them compatible: don't use them to store any new data if the conversion to the old format is lossy: this interface should be used in only one direction, from old to new, but not at all in the reverse direction). You may also choose to converty your old archives to make them conforming (you are not required to use UTF-8, just choose an encoding that is Unicode compliant).
Yes this means some initial cost (for creating the adapter), but there's really no cost (and in fact your save a lot of costs, in money or time, by adopting new softwares instead oif trying to patch more or less correctly an antique software solution that will remain lossy in all cases).
