If you are getting 550 Access Denied SMTP Failure with HELO Name.
Please do the following steps to follow:
For outlook
- Click Tools then E-mail Accounts...
- Select "View or change existing e-mail accounts" and click Next
- Select the email account and click Change
- Click on "More settings"
- Select "Outgoing Server" tab
- Tick "My outgoing server (SMTP) requires authentication"
- Select "Use same settings as my incoming email server"
- Click Ok
- Press Next
- Lastly, press Finish