This article explains how to correct the error message 530 SMTP authentication is required when attempting to send an e-mail through an e-mail client like Outlook Express or Mozilla Thunderbird.
This article applied to Shared Hosting and Reseller accounts and Dedicated Servers.
In order to send e-mail securely through our mail servers, the SMTP authentication option needs to be enabled within your e-mail client software.
The exact method for doing this differs depending on the software used. Instructions for configuring SMTP authentication in Outlook Express are below:
Click the Tools menu at the top of the window and then click Accounts.
Click the Mail tab on the resulting Internet Accounts Window, and select your Donhost e-mail account
Click Properties to open the Properties dialogue box for your Donhost e-mail account
Under the Outgoing Mail Server heading, check the My Server requires authentication box and click OK