Error 530 validating sender
This table lists the SMTP Error codes that are generated along with bounced mail or other common email failures.These messages might also be seen on the Message Audit report generated in the Control Console.If DNS servers are intermittently failing, the verification you perform at that moment may not be indicative of the performance at the time the message was sent.If this error has happened when mail was being sent to your domain filtered by the Mc Afee service, this indicates that we are not able to reach your Inbound Server.
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This error occurs when there is a problem in delivery of the email message.
It indicates that the mail server was reachable and started reception of the message but terminated the delivery before the message transaction could be completed.
SMTP is the protocol (standards that computers use to communicate with each other) that most email servers use to send email messages across the Internet.
When you use an email program, such as Outlook, that lets you store your email messages on your computer, you need access to an SMTP server to send email messages.