My Exchange 2007 or 2010 does not accept emails larger than 10MB. What can I do?

This is due to the default limit of 10MB in the Exchange 2007 receive connector. You can find this setting in the Exchange Management Console under Server Configuration, Hub Transport, Receive Connectors, Properties of the Default Receive Connector:

The Maximum message size is fixed to 10240KB (10MB) by default on the General tab of these properties Change that to 102400 (100MB) in order not to allow longer emails to come through. You can always limit individual user’s allowed maximum email sizes.

You can also use the Exchange Management Shell: View current limits with the Exchange Management Shell command

get-receiveconnector | select identity,maxmessagesize
and change them with
set-receiveconnector "Connector Name (from above)" -maxmessagesize 50MB
set-receiveconnector "*default*" -maxmessagesize 50MB
to 50MB for example.