Up until today this was not a problem. Suddenly, when users attempt to send e-mails from CRM web app to an e-mail address other than one used by our company (i.e. @yahoo, @gmail, @hotmail) the message fails to send. CRM shows it as pending and the event log on the CRM server shows the following error:
System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay
Again, this was not the situation yesterday. All e-mails went through then. It only happens when the recipient is outside of our network. Any recipient inside our network receives the e-mail.
Any thoughts? Thank you in advance.