Dovecot-2.2.1 does not appear to support URLs specified via non-synchronizing literals (RFC 2088 LITERAL+), and also does not read and discard the literal+ input after reporting the error. This results in the literal+ input being interpreted as IMAP commands, which could alter the user's mail store in unexpected ways and/or lead to the abrupt disconnection of the client for exceeding the maximum number of bad IMAP commands.

Example using dovecot-2.2.1 (note that the text nonsync literal includes the invisible CRLFs: "foobarCRLFbarbazCRLF"): a3 append inbox catenate (url {9+} /some-url text {16+} foobar barbaz ) a4 noop a3 BAD Error in IMAP command APPEND: Invalid arguments. foobar BAD Error in IMAP command : Unknown command. barbaz BAD Error in IMAP command : Unknown command. ) BAD Error in IMAP command : Unknown command. a4 OK NOOP completed.

Example using Apple's enhanced dovecot in OS X Server: a3 append inbox catenate (url {9+} /some-url text {16+} foobar barbaz ) a4 noop a3 NO [BADURL /some-url] missing or invalid uid a4 OK NOOP completed.

I believe the RFCs indicate that nonsync literal URLs should be permitted. RFC 4469 section 5: append-data =/ "CATENATE" SP "(" cat-part *(SP cat-part) ")" cat-part = text-literal / url url = "URL" SP astring RFC 3501 section 9: astring = 1*ASTRING-CHAR / string string = quoted / literal RFC 2088 section 4: literal ::= "{" number ["+"] "}" CRLF *CHAR8