SMTP error, Mails aren’t received and there are mails in the badmail folder

SMTP error

Mails aren’t received and there are mails in the badmail folder

Download smtpdiag tool;

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=11393

SMTPDIAG "sender address" "recipient address" [-d external DNS] [/v]