The error "Unroutable address / Unroutable mail domain" is a general error which can be caused by several things:

•     a misspelled email address; for example, you have sent the mail to friend@sitegrond.com instead of friend@sitegroUnd.com; please check very carefully the spelling of the email address of your recipient and try sending the message again;
  

•     you have exceeded the maximum number of e-mails allowed to be sent out per hour; in this case you should allow some time for the number of sent messages to be reduced and then resend the mail;
  

•     the mail server cannot determine the correct route for sending your email message because of a DNS configuration error with the recipient's MX records; in this case the support for the remote server should be contacted for additional assistance

   

  SiteGround provides the best email hosting and our support team will help you with any email questions/problems you have.