the low-level sendCommand(command, args) in FTP, POP3, NNTP and SMTP appends the caller-supplied args straight onto the command line before the trailing CRLF, so an embedded CR or LF in something like an FTP path, a POP3 USER/PASS, an NNTP newsgroup or an SMTP reverse path smuggles a second command onto the control connection. i noticed it reading the sendCommand chain after the SimpleSMTPHeader work and it looks like the same CRLF-injection hole, just one layer lower. fix rejects CR/LF inside each command builder with IllegalArgumentException, which is where it belongs since the message is assembled there, and matches the existing header guards. tests cover each protocol.