Did you get error message as below?

The message could not be sent because the server rejected the sender's e-mail address. The sender's e-mail address was 'name@domain.com'. Subject 'name@domain2.com', Account: 'mail.domain.com', Server: 'mail.domain.com', Protocol: SMTP, Server Response: '550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC78

It's because you have improperly setup your outlook smtp settings for outgoing mail.

Please make sure you have authentication turned ON for the outgoing mail. Go into the advanced settings and for the outgoing server, and check "Outgoing server requires authentication, use same settings as incoming server" - that should solve your issue.

Microsoft Outlook

1. From the Menu Bar, Click Tools then Click E-mail Accounts
2. Select "View or change existing e-mail accounts" then Click "Next"
3. Select your Email account then Click "Change"
4. Click "More settings"
5. Select "Outgoing Server" tab
6. Select the box beside "My outgoing server (SMTP) requires authentication"
7. Select "Use same settings as my incoming email server"
8. Click "Ok"
9. Click "Next"
10. Click "Finish"

And if you continue to experience any problems, you are more than welcome to open a support ticket at https://clients.ionbytes.net/submitticket.php