I've just dealt with for the fifth time on various machines an issue with Outlook 2013 running on Windows 10. One of these times was on my own home machine but after dealing with my neighbours last night, I guess its worth putting up something about here so others can see if it's searched upon.

These machines have been running Windows 10 and Outlook 2013 for sometime, all configured to send e-mail using IMAP connecting to a service like Gmail and everything works as expected then suddenly for no reason e-mails are received ok but when trying to send, messages get stuck in the Outbox and an error is generated. What is bizarre; is that on the Account Setup screen you can send and receive the Outlook test message but your messages stay stuck in the outbox.

A bit of googling, came up with several suggestions, but the one that has fixed it on all occasions for me is the following:

1. Open up an Administrative Command Prompt

2. Type sfc /scannow and hit return. It may take a while for this process to complete

Hopefully, all will be well after this. To quote Microsoft:

The sfc /scannow command will scan all protected system files, and replace corrupted files with a cached copy that is located in a compressed folder at %WinDir% \System32\dllcache. The %WinDir% placeholder represents the Windows operating system folder. For example, C:\Windows

My brother in law who had this issue noticed it after doing a round of Windows 10 updates - so something could be breaking essential systems files? The SFC command appears to put everything back in order.

On another note, I've had an interesting issue with Gmail when I went to setup my daughters laptop some time ago. Again, trying to connect to Gmail via IMAP just refused to work, and the problem in this case was that an option within the Gmail preferences was switched OFF which is to allow unsecured applications access to email. Once switched to ON, Outlook 2013 could quite happily connect to the mailbox again happily. Would seem that Google don't trust Outlook 2013 as a secure enough client!

Hope it helps someone!

Pete