Emails delayed or not received.

If the message left your environment OK, there's not a lot you can do. If you can work with the admins at the recipient company, then you can get them to investigate the message routing and any services that might have quarantined the message on their end and see why (it might require work on their end or work on your end depending on the results). If you can, try get a copy of the message header for a message that was delayed from someone who received it and see what path it took and how long each hop was.