I have been having this issue for over a year now.
The Cox SMTP Server Settings are not working in Outlook 2016. I can receive e-mails via imap.cox.net but, I cannot sent e-mails via smtp.cox.net.
I have tried many many settings with no success.
Please fix this issue immediately.
Chris Peterson
Task 'CCP Mailbox 1 - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).'
Task 'CCP Mailbox 3 - Sending' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP). The server responded: 550 5.1.0 <> sender rejected'
Are you using POP or IMAP? What ports and certificate are you using for SMTP?
Outlook has multiple locations to enable authentication and encryption. Mine has the following separate checkboxes:
Requires Logon Using Secure Password Authentication (SPA)
My Outgoing Server (SMTP) Requires Authentication
This Server Requires an Encrypted Connection (SSL)
You need to navigate through your account settings to find them.
This is another approach: setup your account via Control Panel as opposed to Outlook.
I forgot I had this problem a few years ago with Windows XP Pro. Professional versions of Microsoft are domain-oriented so the OS becomes more involved with Security Management...as opposed to just the application. When Cox required us to change SMTP ports, I couldn't get Outlook to send email.
answers.microsoft.com/.../59e9c3c3-b3a7-49fe-a2b0-758258966c3e
