try: "anonymous,anonymous" for that "username,password" part. (Don't forget your ":21" after the IP address and before your user/pass.)
MORE DETAIL THAN YOU PROBABLY EVER WANTED:
For grins and giggles, did a quick Wireshark sniff of the communication from my Windows PC when doing that "ftp -A server_address" you mentioned, to see what it does. It just used: "anonymous" for the username and "mylogin@PCname" for the password.
FYI this "password" was also echoed back as part of the login greeting that looked like this:
ftp -A ftp.opto22.com
Connected to ftp.opto22.com.
220-Welcome to Opto 22's FTP Server.
220-Please contact Support@Opto22.com, 1-800-835-6786
220 to get a secured account.
331 Password required for anonymous
230 Logged on
Anonymous login succeeded for mylogin@PCname
I found this link helpful too, especially the quote below:
What is Anonymous FTP?
Anonymous FTP is a means by which archive sites allow general access to their archives of information. These sites create a special account called "anonymous". User "anonymous" has limited access rights to the archive host, as well as some operating restrictions. In fact, the only operations allowed are logging in using FTP, listing the contents of a limited set of directories, and retrieving files. Some sites limit the contents of a directory listing an anonymous user can see as well. Note that "anonymous" users are not usually allowed to transfer files TO the archive site, but can only retrieve files from such a site.
Traditionally, this special anonymous user account accepts any string as a password, although it is common to use either the password "guest" or one's electronic mail (e-mail) address. Some archive sites now explicitly ask for the user's e-mail address and will not allow login with the "guest" password. Providing an e-mail address is a courtesy that allows archive site operators to get some idea of who is using their services.
Hope that helps!