contact us page emails not receiving. Error sending e-mail. Mailbox unavailable. The server response was: From domain must match authenticated domain

Hi All,
I have set up the email configuration properly and i have tested it some time back which worked fine, but today i tried to send a test email to myself using the contact us page and it was not sending when i checked the message queue. When i use the "Send Test Email " it works fine, and when i receive an email directly to the email for ex- [email protected] i receive those too but

the log says
Error sending e-mail. Mailbox unavailable. The server response was: From domain must match authenticated domain

full message
System.Net.Mail.SmtpException: Mailbox unavailable. The server response was: From domain must match authenticated domain at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at Nop.Services.Messages.EmailSender.SendEmail(EmailAccount emailAccount, String subject, String body, String fromAddress, String fromName, String toAddress, String toName, String replyTo, String replyToName, IEnumerable`1 bcc, IEnumerable`1 cc, String attachmentFilePath, String attachmentFileName, Int32 attachedDownloadId, IDictionary`2 headers) at Nop.Services.Messages.QueuedMessagesSendTask.Execute()

Thanks in advance
Kli