Java FTPSClient Implicit Mode 550 Error

Scenario

550 errors when connecting to an FTPS client in implicit mode using apache commons FTPSClient library.

Solution

Set execPROT:

execPBSZ(0)
execPROT("P")

Example to connect and upload a file:

import org.apache.commons.net.ftp.FTPSClient

new FTPSClient("TLSv1", true).with {
  connect "localhost", 990
  execPBSZ(0)
  execPROT("P")
  login "user", "pass"
  setControlEncoding("UTF-8");
  enterLocalPassiveMode()
  setFileType(FTP.ASCII_FILE_TYPE)
  setFileTransferMode(FTP.ASCII_FILE_TYPE)
  changeWorkingDirectory ("/home/user")
  def stream = new BufferedInputStream(
    new FileInputStream("file.txt"))
  if (stream.available() == 0) {
    throw new Exception("Cannot read local file stream!")
  }
  result = it.storeFile(destFilename, stream)
  stream.close()
  logout()
  disconnect()
}

Note: Connecting with lftp:

You'll need data-protection as well:

lftp -e "set ftp:ssl-protect-data true; put -O / /file/to/upload.txt; bye” -u user user,pass ftp://ftp.host.com