For POP3 a parameter of 1 tells the library to list the email message or messages on the POP3 server. This can be used to change the default behaviour of libcurl, when combined with a URL that contains a message ID, to perform a "scan listing" which can then be used to determine the size of an email.
Note: For FTP this causes a NLST command to be sent to the FTP server. Beware that some FTP servers list only files in their response to NLST; they might not include subdirectories and symbolic links.
Setting this option to 1 also implies a directory listing even if the URL doesn't end with a slash, which otherwise is necessary.
Do NOT use this option if you also use
#CURLOPT_WILDCARDMATCH as it
will effectively break that feature then.