I have the max send/receive file size set at 75MB each. When i try to send a 10mb PDF from outlook to a gmail account i get the undeliverable message.
You may be sending it ok, but gmail could be rejecting it as it is over their max (25MB) (Note it is possible for a 10Mb Pdf could be encoded in such a way that exceeds 25MB)
Also, there are various different limits in Exchange 2007. You can limits on the individual user's mailboxes and you can also have limits on the send connectors.