Change Port Number to 587
Step 1: Start your Outlook. Click Tools and go to Account Settings.
Step 2: Under account settings, click the change button. Go to more settings under add new email account. Click on the tab, labeled "Advanced."
Step 3: Go to the port numbers of SMTP and IMAP, set 587 as the port number for SMTP (Outgoing server). Now click, Ok. Click on Next and then the finish button.
Step 4: Close your outlook application and restart it. Try sending a message and see if it works. If the error pops up again, move to the next method.
Greetings,
Peter