Error 0x800CCC67 in Outlook

I am using Windows 10 Home, Microsoft Outlook - part of Microsoft Office 2007 and Avast Program version: 11.2.2262, Virus def. version: 160504-4

When I send and receive emails in Outlook I get the message
Task ‘*****@gmail.com - Sending’ reported error (0x800CCC67) : ’ The server responded: 421 Cannot connect to SMTP server 64.233.189.108 (64.233.189.108:587), connect error 10060’

If I disable Avast shields emails are sent and received OK.

I have been using the same set-up for over a year and this is the first time I had this problem.

I have checked and Windows and Avast are all up to-date.

Welcome to the forum.
I don’t use Outlook but suggest that you try the following:

Open Outlook click on File > Account Settings > Email > ‘More Settings > Outgoing Server
and check the option which reads ‘My outgoing server requires authentication’.
Apply the settings and restart Outlook.

Thank you for your reply.

Yes I have 'My outgoing server requires authentication’ checked.

As I said in my original post I have been using the same set-up for over a year and until today it has worked. As disabling Avast allows emails to be sent and received points to the problem been with Avast.

File a support ticket to get help directly from Avast:
http://support.avast.com/support/tickets/new