For some reason, my board will not send email. I;m trying sending the Administrators an email through the control panel, but every time I do, t logs the following error:

SendMailThread failed with an SmtpException (Email to: xxx@xxxx.com, Subject: another test): System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: No such user here
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 YAF.Core.Services.YafSendMail.SendAll(IEnumerable`1 messages, Action`2 handleException)

But I know the email exists because I use it on a regular basis. Any ideas what should be looking at?

Never mind, I found the issue. I had a ms-matched "from" address in the board settings.