Many times you will get “Invalid domain name” error especially during sending mails. It could be that the DNS host or domain name contains invalid characters and therefore, it is important to you check that the DNS host name and the DNS domain name contain contains only valid characters.
It should be noted that the valid characters for the DNS host name and the DNS domain name are letters A-Z, numerals 0-9, and the hyphen. However, there are also some instances that the period contributes a part for preventing an invalid domain name message since this is also used as a separator. If you get the error message you need to wait for some time to allow domain name resolution. If that still does not fix your problem, you should contact your domain registrar and inform him of the problem.