When i am trying to execute the 'Send mail task' alone or package alone its running perfectly. but when i am trying to shedule it. i am getting an error like shown below.
Description: An error occurred with the following error message: "Mailbox unavailable. The server response was: 5.1.1 User unknown". End Error DTExec: The package execution returned DTSER_FAILURE (1). Started: 6:00:01 AM Finished: 6:11:46 AM Elapsed: 705.125 seconds. The package execution failed. The step failed.