This evening I took the Windows 10 upgrade plunge… I “sat back and relaxed” as ordered, and all was going swimmingly – the kids oooo’d and ahhhh’d as we tried things out, and we all said it looked like how Windows 7 and 8 should have really been, etc etc, until I tried to send an email from Outlook 2013. Nope. Stuck in the outbox. Rebooted. Nope, stuck in the outbox. And this is using a Microsoft hotmail (aka live) account (aside: sending using a work Outlook 365 account worked fine).

After a bit of binging and even some googling I ran sfc /scannow from an administrative command prompt and got this:

and the moment I re-started outlook my emails were sent, yay.

The fact that others were reporting this during testing of early beta releases of W10 makes me think they could have built this fix into upgrade, but there we go. Hope this helps someone.