Businesses can use Gmail to host their emails but if you get a 550 error then here are the steps to correct this.
If you get a response as follows:
550 Please turn on SMTP Authenticationin your email client. [209.85.160.43] is not permitted to relay through this server without athentication.
The server is rejecting outgoing emails because your email client has not presented valid login credentials.
1. Turn on SMTP Authentication in Gmail.
Login to Gmail.
Click on the setting icon on the top right.
Select see all settings.
Go to Accounts and import.
Click on the edit the email and check all the settings, if not, then re add your email address.
In the send mail as section click on “Add another email address”.
Enter email address.
Send through Gmail and click next step.
Enter the SMTP server provided by your host i.e. mail.website.com
Email and password.
select secured connection using tls and click add account.
The port must be 465, SSL and authenticated
Port 465 is the correct port to use for security, so ensure this is set correctly.