For other error codes, see List of Outlook error codes.
Problem description
When using the Outlook client, you can receive emails but cannot send them. Error code 0x800CCC78 appears when you try to send an email.
This error occurs when Outlook cannot authenticate with the outgoing mail server (Simple Mail Transfer Protocol, or SMTP). There are two common causes:
Cause 1: Incorrect account or password
The SMTP server rejects the sender's address because authentication fails. The error message reads:
This message could not be sent because the server rejected the sender's email address. The sender's email address was "a***@example.net", Subject: 'sfdsdf', Account: 'XXX', Server: 'XXX', Protocol: SMTP, Server Response: '530 Authentication required', Port: 25, Security (SSL): No, Server Error: 530, Error Number: 0x800CCC78Cause 2: Account is blocked
The account is blocked from sending email. The error message reads:
541 This account isn't allowed to send email
Solutions
Enable SMTP authentication in Outlook
Use this solution if the error message contains 530 Authentication required.
Open Outlook and choose Tools > Accounts.
Select the affected account and click Properties.
Click the Servers tab, select My server requires authentication, and then click OK.
Restart Outlook and send a test email to confirm the issue is resolved.
Change your password and contact your administrator to unblock the account
Use this solution if the error message contains 541 This account isn't allowed to send email.
Change your password and contact an administrator to unblock the account. For more information, see What do I do if my Alibaba Mail employee account is blocked or frozen?
After the account is unblocked, send a test email to confirm the issue is resolved.
Applies to
Alibaba Mail