Unless your ISP offers IMAP access (for an IMAP client like Pegasus or Thunderbird, but NOT Mercury) then yopu will need to log onto the webmail interface and copy any mail you want from the subfolders into the INBOX, then POP-ing via Mercury will collect it.
Unless your ISP offers IMAP access (for an IMAP client like Pegasus or Thunderbird, but NOT Mercury) then yopu will need to log onto the webmail interface and copy any mail you want from the subfolders into the INBOX, then POP-ing via Mercury will collect it.