Mailbox unavailable. smtpclient

Question

Hi Team, I have one issue with sending email thr smtpclient, some time i got error MailboxUnavailable , Reason : Mailbox unavailable. The server response was: 5.1.1 , but after some time or next day i can send this email., what i need to check,please help.

Rajeesh Menoth · Answer

Hi,   Please check the sending email is a valid one because most of the answer is mentioned "wrong recipient address" !!   Reference :   https://social.technet.microsoft.com/Forums/en-US/c1d8891c-c19b-48dd-85ff-a28f7e61cef9/511-smtp550-511-user-unknown?forum=exchangesvrdeploylegacy   Mark as answer, if that helped you

sandip bin · Answer

Client use  exchange server, not send bulk email but send email using batch binary contineously      Thanks for reply.

Amit Gupta · Answer

Which SMTP server are you using?    Are you sending bulk emails? If yes, then make sure that service provider is allowing that service.   Ask your server provider for the issue. There might be issue from there end.