Downloading large files (then considered to be over a few megabytes) was nearly impossible due to bandwidth limitations, as well as frequent errors and lost connections.
It also allowed people who accessed the Internet only through email using dial-up lines to download files that were located remotely.
Unlike FTP, files could be transferred through FTPmail even if the user did not have an online Internet connection (for example, using BBSes or other specialized e-mail software).
FTP also has lost popularity in favor of other methods for file transfer, notably HTTP which is available to virtually all Internet users.
The server then processes the request by logging on to the remote site, retrieving the file, encoding it, and returning the result via email.