Assigning multiple labels (X-Label) to a message

[Kurt Hackenberg]

On 2020-12-16 13:05, Kevin J. McCarthy wrote:

> Mutt's label handling is pretty basic right now.  It expects only a 
> single X-Label header in the email.  When editing the label, Mutt only 
> knows how to write a single X-Label header back.
...
> The label completion has some code to delimit by ":" or ",". However, 
> internally Mutt doesn't understand the multiple values, making the 
> completion less then useful.

Some mail programs use X-Keywords, which I think can have multiple 
keywords separated by whitespace. Pine and Dovecot use that header, that 
I know of. My knowledge is fragmentary, and these headers are 
non-standard, so not well defined.

I don't know of anything other than Mutt that uses X-Label, but I don't 
know much.

One possibility would be to keep X-Label, add X-Keywords, and make the 
first value from X-Keywords be the only value of X-Label. That would 
attempt to maximize compatibility with other software.

How does Mutt handle this through IMAP? The protocol knows about 
keywords. Dovecot, using maildir, can store multiple keywords as 
metadata, outside the message file contents. That's a non-standard 
extension of maildir, though.

What about when Mutt handles maildir directly? Still X-Label in the message?