You are getting this message because your ISP's / Web Hosting providers mail server requires you to enable "SMTP Authentication"Â. Below is the error you are most likely getting:
-- Error Code Example -- SMTP error from remote mail server after RCPT TO::
host mail.yourdomain.com [64.239.33.14]:
553 sorry, that domain isn't in my list of allowed rcpthosts; no valid cert for gateway (#5.7.1)
Ways to resolve the problem (Microsoft Outlook):
1. Click Tools then Email Accounts (Accounts and Services on older versions of Outlook)
2. Click View and Change and Click Next (skip if it opens up to the account screen)
3. Click Change or Properties of your Email Account
4. Click More Settings
5. Click Outgoing Server
6. Check My Server Uses Authentication
7. Select Log on Using
* Type Account Name (which will be your full email address)
* Type Password (which will be your email address password)
8. Click OK
9. Click Next
10. Click Finish
This should fix the Outlook to send email. Close Outlook and re-open it to start sending mail.
