Technical information concerning the bpost FTPS connection.
Making an FTPS connection is similar to making an FTP connection, but it includes an additional security encryption method ‘TLS/SSL Explicit encryption’ to be chosen at the time of creating the connection.
bpost FTPS host name: filetransfer.bpost.be
Don't forget to cross check that the below configuration is available on your firewall/proxy
Allow connections to port 21 for TLS/SSL
Allow traffic to passive port range 30000-40000 for TLS/SSL
The document attached below, gives a step-by-step guide to make an FTPS connection using FileZilla or WinSCP (file transfer clients).