When e-mailing attachments via MS CRM 3.0 there have been a few posts about the limit in attachment size. This is by design and is set 5mbs
for those who have a nice beefy system for MS SQL and don't mind letting their users have a ton of power for clogging up the net ... ok, ok.. who have thought carefully about what they want to send you can
By making a change to the Registry...
On the Server
On the Client
Warning.. If you are messing with the registry then you should understand that this entails risk. Really you can mess things up. So don't mess with the registry if you don't feel really good about what you are doing.
I suspect that you would much rather have these attachments in MS SQL as opposed to the Exchange store if saving them in e-mail is critical.