Invalid `\*` in `FLAGS` response

[link2xt]

More details here:
chatmail/core#1834
djc/tokio-imap#91

[duesee]

Further information:

\*, which means ...

     The PERMANENTFLAGS list can also include the special flag \*,
     which indicates that it is possible to create new keywords by
     attempting to store those flags in the mailbox.

... is only valid in the PERMANENTFLAGS response code. See ...

mailbox-data = "FLAGS" SP flag-list /                             
               "LIST" SP mailbox-list /
               "LSUB" SP mailbox-list /                               
               "SEARCH" *(SP nz-number) /
               "STATUS" SP mailbox SP "(" [status-att-list] ")" /    
               number SP "EXISTS" /                       
               number SP "RECENT"

flag-list = "(" [flag *(SP flag)] ")"

; Does not include "\Recent"                    
flag = "\Answered" / "\Flagged" / "\Deleted" / "\Seen" / "\Draft" / flag-keyword / flag-extension

resp-text-code= "ALERT" /
                "BADCHARSET" [SP "(" astring *(SP astring) ")" ] /  
                capability-data /           
                "PARSE" /
                "PERMANENTFLAGS" SP "(" [flag-perm *(SP flag-perm)] ")" /  
                "READ-ONLY" /                               
                "READ-WRITE" /              
                "TRYCREATE" /
                "UIDNEXT" SP nz-number /                               
                "UIDVALIDITY" SP nz-number /
                "UNSEEN" SP nz-number /  
                atom [SP 1*<any TEXT-CHAR except "]">]

flag-perm = flag / "\*"

[duesee]

Thinking about a low-level solution: We could discard \* in FLAGS and emit a warning. However this won't work when a single \* is send in flag-list because discarding a single \* in flag-list would result in an empty flag-list which is not allowed either. If we would be on some upper layer, we could discard the whole message. But this requires some "signaling mechanism"?

Is this flag when using zoho operationally relevant? If so, should we accept it in FLAGS?

[duesee]

Reading through chatmail/core#1834 more closely, it seems that Zoho has fixed the issue.