To point your Yahoo! Small Business domain to SITE123, you must have access to your domain management panel or be in contact with your domain provider. You will need to update 2 records in your domain settings: A record and CNAME record.
Follow the steps:
Log in to your Yahoo!SmallBusiness account.
Next to your domain, click Domain Control Panel.
Go to your primary A-record and click Edit.
In the Destination field, change the IP address to 126.96.36.199 and click Submit.
If you have another A-record for your domain, please delete it. If there is no such record, ignore this step.
Click Add Record and select CNAME.
In the Source field, enter www.
In the Destination field, enter ssl.site123.com and click Submit.
If you do not want to setup SSL, set the CNAME to point to global.site123.com
Note: Yahoo! Small Business is an external domain service and the steps of connecting your domain may change over time as they update their services.