Neil Romig writes:
Not sure what's changed between Courier 0.75 and 1.0 - but one of the features of the Courier 1.0 release was implementing Unicode email... Neil.
This is correct. Courier 1.0 implemented RFC 6855, and will not deliver messages containing non-ASCII header contents to non-RFC 6855 IMAP clients. RFC 6855 does acknowledge that this will break a combination of misformatted E-mail that does not properly encode headers according to the relevant standards (mostly RFC 2047 and RFC 2231), and non-RFC 6855 IMAP clients; this is discussed at some length in section 7 of RFC 6855. Mail with properly-encoded headers is not affected.
If an non-RFC 6855 IMAP client attempts to retrieve a message with 8 bit unencoded header data, Courier 1.0 will return an error message; mostly one of the options section 7 outlines as the way to handle this situation. There are several ways to indicate an error in IMAP; and the next minor Courier release will tweak this behavior slightly, to hopefully result in a better experience with non-RFC 6855 IMAP clients; but the basics remain the same: messages containing 8-bit header data are presumed to be Unicode messages that can only be correctly be interpreted by clients that enabled IMAP Unicode mode. They are still included in the folder's message index, but attempts to retrieve them will result in some kind of an error.
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