RedHorse CRM itself does not pose any restrictions to the size of attachments. That said there are aspects surrounding sending/receiving large atachments external to RedHorse that might pose a problem. You mentioned free disk space. Another might be that either your mail host or the mail host of the address that you are sending to or receiving from could be placing a limit on email attachment size. Or if the Internet connection is very slow RedHorse might reach the Timeout set for an smtp connection when sending a large file.

There is no size limit on Docs.