I finally seem to have fixed a problem that has apparently been with me for weeks since updating Windows 10, but I have not noticed! Basically, Outlook 2013 was failing to send emails from either of my accounts that used SMTP / Imap (but was working fine for a client email address using an Exchange server).
To confuse matters even more, when configuring the email addresses the ‘Test Send’ email step would work; but nothing else would send, very very quietly sitting in the ‘Outbox’ yet not doing a whole lot to bring the repeated failures to send to your attention (of course, in hindsight I do accept I was missing some clear signs – not least of which my partner telling me she had not received an email I’d sent!). Outlook only ever really makes the sending problem very obvious when trying to close the application… and guess what; I hardly ever do that as I put my computer to sleep a lot, and do not generally shut it down after carefully closing all my apps. I had already tried Repairing the office installation, and a full uninstall / reinstall of Office; but neither of those procedures worked for me.
Anyway, thanks to this Windows Central thread, I have run the command prompt in Admin mode, run the command:
and after a little while of that running, restarting Outlook happily now sends emails!
In case you are wondering, the sfc command says it “Scans the integrity of all protected system files and replaces incorrect versions with correct Microsoft versions.” I have no idea what was wrong, but file replacements were made apparently:
The log file noted in the command output: Windows\Logs\CBS\CBS.log is rather large and non-obvious to me what the significant information in it is!
I’m hugely surprised that I did not notice the outbound problem for as long as I did… it does make me a little more cautious about Windows 10 (I already had to reinstall VMWare Workstation as that had problems with networking after the Windows 10 upgrade too!)
UPDATE 10/12/2015: This fix has now worked for me on a second PC which also had failures sending email from Outlook 2013 after a Windows 10 installation!