This is utterly unbelieveable, but I saw it, and the problem is consistent.
User is on Exchange 365 with Outlook 2010, all patches SP etc....
The user has her email set so that the items in Outbox only send when she tells them to, her reason for this is she is in sales, and she sometimes likes to revise emails. Sounds like a valid reason to me.
So, she will have a few items in her Outbox, then she will open the outbox to see what is in it, then try to send. NONE of the emails that are in sent items will go, if she opens the folder. She does not even have to open the emails , just open the folder.
And, even stupider behavior, if she then creates an email or two, does not open the Outbox, and clicks on SEND, the newly created items will send, and the items that were previously stuck, stay stuck.
She has to open her email in the sent items, copy and paste to a new email, delete the old email in her outbox, then do a send on the email, then click on SEND/Recieve ALL and the emails will go.
I watched this several times. There HAS to be a bug or known issue causing this. Why would an email not leave the Outlook Outbox, just by opening the outbox folder? How could this prevent only the emails that are in the folder from getting sent?