Important Update - This is a Current Google Problem - see my answer
We have recently migrated from an inhouse exchange server to gmail (using google apps for business). The migration has been far from flawless and I'm about to lose my mind! Almost all problems have been corrected and sorted out except for this one which is really confusing.
When our users who are using outlook exclusively (POP3 access to their gmail account) sends an email it will be delivered multiple times.
It appears that the delivery of the additional emails (which are duplicates of the original) hit the recipients inbox again hours after the original was sent.
It is worth noting that at the times the additional emails are delivered outlook has been closed and the machines logged off (and have been for hours).
It's also worth noting that one of our clients mentioned that when they open the email (i.e. double click it in outlook) the received time changes to the time the original email was sent.
Any ideas? (I'm waiting to receive the email headers from one of the 'message chains').