You can use the parameter remove_files to remove the source files.
If the source a FTP server then it is possible that you get the following message in the log although the FTP user has write permission on the source files.
INFO (SOSVfsFtpBaseClass.java:871) ::delete SOSVfs_I_131: File deleted : '/tmp/ftp/out/1.txt', reply is '550 Delete operation failed.
It is possible that the FTP server settings doesn't allow write operations.
Please check the FTP server settings.
Example FTP server (vsftpd) on Suse Linux
You find the settings in /etc/vsftpd.conf. Make sure that write_enabled=YES.
... # ################ # General Settings # ################ # # Uncomment this to enable any form of FTP write command. write_enable=YES # ...