We are in the process of migrating users from Exchange 2007 to 2013 in our environment. We have only moved a select few test users at this time to get all of the problems worked out. Recently we've noticed that users on the new Exchange 2013 server have problems sending excel documents to our users still on the Exchange 2007 server. Below are the type of error messages we are receiving. From the 2013 server we can send those same messages to outside email addresses.
Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept email from certain senders, or another restriction may be preventing delivery.
Remote Server returned '550 5.7.1 Requested action not taken: message refused'
Does anyone have any ideas?