Email sent to self takes 10mins to receive

If I use the Outlook web portal, I get a fairly instantaneous reply to email I send myself.  If, however, I use a Microsoft client like Outlook 2011 for Mac, sending the same email to self takes 10 minutes before it lands in the inbox. This despite constantly pressing "synchronize now" in the email client sw.

Outlook indicates that it sends immediately.

Any ideas why such a huge difference?