Cannot send message (None of the email recipients were accepted by the server)

Cannot send messages, description of log below
10:31:15 [email protected] [SMTP]  Connected: To [email protected]
10:31:15 [email protected] [SMTP]  Sending messages
10:31:15 [email protected] [SMTP]  Sending messages: Recipient address ‘[email protected]’ not accepted due to the following reason: 
10:31:15     "5.7.1 <[email protected]>… Relaying denied: You must check for new mail before sending mail.
10:31:15 "
10:31:15 [email protected] [SMTP]  Sending messages: Recipient address ‘[email protected]’ not accepted due to the following reason: 
10:31:15     "5.7.1 <[email protected]>… Relaying denied: You must check for new mail before sending mail.
10:31:15 "
10:31:15   MailClient.Storage.Application.ItemOperationException: Cannot send message (None of the email recipients were accepted by the server.)
10:31:16 [email protected] [SMTP]  Disconnected: From [email protected]
10:31:16 [email protected] [SMTP]  Disconnected: Done
10:31:17 [email protected] [POP3]  Disconnected: From [email protected]
10:31:17 [email protected] [POP3]  Disconnected: Done