Fix Outlook Cannot Send Email to .co.uk Addresses
Question details
Users are unable to send messages to valid United Kingdom email addresses ending in .co.uk from Microsoft Outlook.
- Product
- Outlook
- Device & OS
- not provided
- Scenario
- Attempting to send an email to a recipient with a .co.uk domain.
- Observed behavior
- The email fails to send, and the user receives an incorrect format error or a nondelivery report (NDR), despite the email address being completely valid.
Verify that the recipient's email address does not contain any hidden spaces, special characters, or missing letters, especially if you copied and pasted it from another document.
Test Sending via Outlook.com Web Access
Isolate the issue by checking if the problem is specific to the Outlook desktop application or an issue with the account itself by using the web browser version.
Comparing the web experience with the Outlook application can determine whether the problem is caused by the app cache, an account limitation, or recipient-address validation issues.
Open your preferred web browser, navigate to Outlook.com, and sign in with your email credentials.
Click the 'New Message' button to start drafting an email.
Carefully type the problematic .co.uk email address into the 'To' field without pasting it.
Send the email. If it goes through successfully, the issue lies within your Outlook desktop app settings or cache.
Clear the Outlook Auto-Complete Cache
Remove corrupted or improperly formatted email entries from the Outlook app's memory.
Switch to WPS Office for a Smoother Productivity Experience
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Frequently Asked Questions
Why does Outlook say my valid .co.uk address is in an incorrect format?
This usually happens due to a glitch in the Outlook Auto-Complete list, hidden special characters copied with the email address, or strict validation bugs in certain versions of the Outlook desktop client.
Will repairing Microsoft Office fix this email delivery error?
If the issue is isolated to the Outlook desktop app and clearing the auto-complete cache doesn't work, running a Quick Repair or Online Repair on your Microsoft Office installation can resolve underlying application bugs.
Does a nondelivery report (NDR) mean the email address is fake?
Not always. While an NDR often indicates an invalid address, it can also be triggered by temporary recipient server outages, strict spam filters, or formatting bugs within your specific email application.
