I had something similar recently and resolved it.
It turned out I had ticked the box on Outbound Mail Server Settings to set Outbound E-Mails to use Inbound Mail Box.
On Inbound Email Mappings, I mapped the process to a mapping. But on Inbound Email > Mailboxes, I hadn't associated the mapping to an email address. So the system had no mailbox associated to the process and sent the Object not set error.
Be warned, if this is the issue and you fix it, all emails will be sent suddenly so you might want to clear the Recipient Message table first.
thanks that does seem to have been the problem, i am to embarrased to admit how long i have been banging my head against that one.
No worries. I had exactly the same head banging experience. You were just lucky I clicked the link. We are just thinking of upgrading to 7.5 so I'm trying to look for any major issues within it.
Unfortunately I didn't think to clear the Mail queue and had the effected department moaning at me as they had to put up with 50+ calls/email responses from their customers saying the issue was resolved months ago.