In environments where there either were or where there were expected to be transfers of either large files or large numbers of files, I have used FTP (SFTP / FTPS) to allow for the file transfers. This serves to keep large files/attachments off of your e-mail system while still preserving the collaborative ability of a distributed team (either internal or with your business partner(s)).
The gotcha: you need to either dedicate a server (virtual or physical) or at the very least an area of your SAN as the “drop box” (the transfer area), and the FTP protocol is by definition somewhat less than secure (and I’m being generous). I would suggest using either SFTP or FTPS as they are substantially more secure than plain old FTP.
A good discussion of SFTP vs FTPS and the pros and cons of each can be found here:
There are a variety of FTP clients available, both proprietary and open source: all perform similar functions…