We have a new Exchange 2010 Standard Server setup and have migrated email from Microsoft BPOS. The server has been running for 5 days now and is working well except for one annoying problem. A user will send an email with an attachment to an email address that is external (not in the same domain), they will receive the email but they will either not have the attachments or the attachment will show up but show as a 1k file and when the user tries to open it, they will be prompted to save the file (it will have a strange file name like %000%000%00000%00000%000000) and can't be opened by anything.
Many external addresses can see the attachments and open them just fine. This only happens to a few people. They are on different domains so it is not just one email server that is having an issue. I can send the same attachments to the same recipient from a different address (not on the exchange 2010 server) and they will see the attachments and be able to open them.
The server has Windows Server 2008 R2 on it with Exchange 2010 Version: 14.02.0247.005.
Although not recommended, the server is a domain controller. There is no other software on the server except for backup software. I don't believe that Exchange does any sort of outbound email filtering by default but I have turned off the Exchange Spam filter for incoming email. This is the only Exchange server for this domain (all exchange roles are on this server).
The problem occurs when sending from outlook or from OWA.
It happens the same from multiple internal email addresses.
I believe that the issue must be in the way exchange is formatting the emails and some of the clients have an issue reading the attachments when in this format.
All suggestions are welcome. This is starting to become a big problem. Thank you for any help.