If you wanna send file to server from local host computer,You must sarch for the FFFTP program on sarch engin.
And then your sever's FTP port is opened by port 20 and 21.
Then server's drive is named for / .
/ drive have the directory of www.
www folda have account name's folda.
And the folda is set for password and ID that can open for ftp soft wear.
The ftp is set to ID and ftp server name and ID and host's directory name and server's directory and pas/v mode and more.
So later the server can access for local host on ftp soft to ftp port.
I think iTunes store and apple music that is set ftp to guest's computer or smart phone's music folda.
FTP softwear is highest secure of trance file that is html, movie, audio, txt, dat, exe, cgi, pl, php and more.
So apple can easy look up for trafic of access to ftp port.
And mail server have been opened for port of recieve is 110,and send is 587 or other port number.
But mail port can come and go for short file of anything.
If You must trance big size file,you would better to choose ftp.
Thank you!