When we send emails with the Send an Email link, the emails always go as text/plain, 7bit, us-ascii, while we simply put there anything the user/dabatase provides.
1. properly encode the headers (as headers cannot include non-US-ASCII characters, they must be quoted-printable encoded; also, header lines can?t be longer than 75 characters, so longer ones should be wrapped), and either
2a. describe the contents of the email as UTF-8, 8bit encoded, which will work (and be true), but not exaclty perfectly compliant with RFC, or
2b. recode the contents of the email to the smallest charset containing all of the characters used in the email and then describe the contents accordingly (be it US-ASCII, ISO-8859-1, ISO-8859-2, UTF-8 or anything else).
I believe we should go with 2a. first, then 1., then consider implementing 2b.