More on the issue of blank invites, just received:
MailMate will be handling it in the next update. But the point is that Discourse is producing an illegal character set descriptor according the MIME spec.
en_US is a language, not a character set, and it makes no sense in this context. Sure, everyone has to handle it, but that doesn’t mean it shouldn’t be fixed, and if a mail program can’t parse that, it’s going to default to
us-ascii rather than
utf-8, because that’s the default for that content-type.
(MailMate is a markdown-based, extremely customizable, Mac IMAP client.)