If you see errors like the below
Message delivery to the host 'xxx.xxx.xxx.xxx' failed while delivering to the remote domain 'terra.com.pe' for the following reason: An SMTP protocol error occurred. The SMTP verb which caused the error is 'HELO'. The response from the remote server is '504 <xxxxx>: Helo command rejected: need fully-qualified hostname
Then setup your fully qualified domain name.
Administrative Tools > IIS Manager -> HOST -> Default SMTP -> right click Properties -> Delivery -> Advanced -> full-qualified domain name