An unknown error has occurred Outlook Mail SMTP Error 0x800CCC67

You may get SMTP Error as An unknown error has occurred Outlook Mail SMTP Error 0x800CCC67 in Microsoft Outlook or Windows Live Mail. Usually it occurs when you try to send an email from Microsoft Outlook or Windows Live Mail. As we observed most common reason for this issue would be changes or updates in SSL or Port settings. And Anti-Virus or Firewall blocking SMTP access.

An unknown error has occurred Outlook Mail SMTP Error 0x800CCC67

This issue may occur if one of the following scenarios is true:
  • Your Outlook might be disconnected or not connected to Internet.
  • Incorrect settings of Outlook mail account.
  • Incomplete installation of Outlook
  • Incorrect configuration of Antivirus software
  • When your Outlook user profile is damaged.
  • If Outlook email item on your POP3 server is damaged.
  • When Outlook is removed or installation of Outlook is damaged.
When you attempt to send or receive email, you see one of the following error messages. 
  • An unknown error has occurred. Subject ”, Account: ‘mail.isot.com’,
    Server: ‘mail.isot.com’, Protocol: SMTP, Server Response: ‘421 mail.isot.com
    connection refused from [66.187.86.1]’, Port: 25, Secure(SSL): No, Server
    Error: 421, Error Number: 0x800CCC67

An unknown error has occurred Outlook Mail SMTP Error 0x800CCC67

To resolve this issue, use one or more of the following methods. After you complete each method, send yourself a test email message to make sure that you can send and receive messages without receiving an error message. If you continue to receive errors, try the next method.

Quick Note: Before making any changes in your computer, I suggest you to create a System Restore point  so that you can restore back your computer to previous working stat if something goes wron.

Step 1: Make sure that you are connected to the Internet and able to telnet SMTP port number.

assets folding start collapsed To do this, follow these steps:

  • Start an Internet browser.Or ping the google.com; ping www.google.com. You should get reply as below if the computer connected with Internet.

Telnet’ing the SMTP port :

  • Type command as telnet smtp.servername.com 25.
  • Example: If you have a google domain account. The telnet command should be: telnet smtp.gmail.com 25.

  • You will get the reply as below If not contact ISP (Internet Service Provider).

Step 2: Make sure that your Outlook email account settings are correct.

Incorrect email account settings can also cause the issues. We have listed some major Internet Service Providers settings (for manual configuration of Outlook)

We recommend that you contact your Internet service provider (ISP) for information about the exact incoming and outgoing mail server names and settings that you should use when you configure your Internet email account in Outlook. The list provided here contains information only for some Internet service providers in the United States and may not be up to date.

Incoming Mail (POP3) server names and settings:

Provider Name Server Name Port SPA SSL AuthRequird
AOL pop.aol 110 OFF OFF ON
AT&T Yahoo pop.att.yahoo.com 995 OFF ON ON
Charter pop.charter.net 110 OFF OFF ON
Comcast mail.comcast.net 995 OFF ON ON
Cox pop.[insert region].cox.net 110 OFF OFF OFF
Gmail pop.gmail.com 995 OFF ON ON
Juno pop.juno.com 110 OFF OFF OFF
Microsoft Live pop3.live.com 995 OFF ON ON
Netscape pop.3.isp.netscape.com 110 OFF OFF ON
Netzero pop.netzero.com 110 OFF OFF ON
Pacbell pop.att.yahoo.com 995 OFF ON ON
PeoplePC pop.peoplepc.com 110 OFF OFF ON
Qwest pop.[enter state ID].qwest.net 110 OFF OFF OFF
Rogers pop.broadband.rogers.com 110 OFF OFF ON
SBCGlobal pop.att.yahoo.com 995 OFF ON ON
Swbell pop.att.yahoo.com 995 OFF ON ON
Verizon incoming.verizon.net 110 OFF OFF ON
Yahoo pop.mail.yahoo.com 110 OFF OFF OFF

Outgoing Mail (SMTP) server names and settings:

Provider Name Server Name Port SPA AuthRequired Encryption
AOL smtp.aol.com 587 OFF ON None
AT&T Yahoo smtp.att.yahoo.com 465 OFF ON SSL
Charter smtp.charter.net 25 OFF ON None
Comcast smtp.comcast.net 587 OFF ON TLS
Cox smtp.[insert region].cox.net 25 OFF OFF None
Gmail smtp.gmail.com 587 OFF ON TLS
Juno authsmtp.juno.com 587 OFF OFF None
Microsoft Live smtp.live.com 587 OFF ON TLS
Netscape smtp.isp.netscape.com 25 OFF OFF None
Netzero authsmtp.netzero.com 25 OFF ON None
Pacbell smtp.att.yahoo.com 465 OFF ON SSL
PeoplePC smtpauth.peoplepc.com 587 OFF ON None
Qwest pop.[enter state ID].qwest.net 25 OFF OFF None
Rogers smtp.broadband.rogers.com 587 OFF ON None
SBCGlobal smtp.att.yahoo.com 465 OFF ON SSL
Swbell smtp.att.yahoo.com 465 OFF ON SSL
Verizon outgoing.verizon.net 25 OFF ON None
Yahoo smtp.mail.yahoo.com 25 OFF OFF None

Step 3: Disable or uninstall anti-virus.

Check your antivirus manufacturer’s website for additional suggestions or Disable the antivirus software. And Disable the firewall in router. If you found outlook is working fine after disable the antivirus software, highly recommended to uninstall the same using their removal tool and reinstall it.

Follow below links to disable, uninstall or reinstall antivirus software from your computer

List of manual antivirus uninstallers:

Click the link associated with the antivirus software currently installed on your system and follow the prompts or instructions on the website. After uninstall, reboot the computer.

Step 4: Create New Outlook Profile and Reconfigure email client.

  • Go to Control panel, Click on Mail Option.
  • Click Show Profiles
  • Click Add
  • Type a name for your profile.
  • Outlook 2007 and above versions support “AutoDiscovery“. This will set up your email account automatically. Enter your name, email address and password and Outlook will try to set up the profile. If it does not work, proceed with “Manually configure server settings or additional server types” and continue.
Refer below links to create Outlook Profile and Mail Configuration.
Conclusion:

Hope above resolutions steps helped you to fix the An unknown error has occurred Outlook Mail SMTP Error 0x800CCC67 issues. If not you need to contact your email providers or Internet service provider. Meanwhile ask your queries in comments or Forum.