Hi Daniel, kindly follow the steps below to get this resolved;
Step 1: Click on File. This is at the top of the program banner. Now click on the resulting "account settings" in the drop-down menu. You may need to click the file, then info to see account settings in some versions of Outlook.
Step 2: Click the email tab under account settings. After clicking the email tab, your email address would appear.
Step 3: Double click on your email. After double-clicking on your email, new windows would pop up, now click on outgoing to go to the right setting.
Step 4: Check your Outgoing Settings: Here, you need to ensure two of the settings are set properly. Two of these settings are important and must be checked so Outlook can work properly. Check the following boxes
"My outgoing server (SMTP) requires authentication."
Click the bubble named "Use same settings as incoming mail server" or if you have that option missing, simply ensure the information on outgoing and incoming mail server are the same.
Step 5: Now click on, ok. Go back to your email after clicking ok. Please do not test account settings. This won't work and can undo some settings. Click Finish and then close to leaving account settings.
Note: Some versions of Outlook may look slightly worded. Just ensure you don't click "cancel".
Step 6: Restart Outlook and then try sending an email. Now after restarting your Outlook, try to send out a message and see if the error shows again. If the error comes up back, try moving to the next method.
Thanks, hope this helps
Nelson...