It needs to be an SMTP server. You may need to ask your IT department for the server name. In our TDA 3.0 Beta we have added a feature to help you auto detect the server name, but unfortunately that is not in TDA 2.7.
It seems that it’s not a problem with TDA but rather some network configuration issue. Please try the following:
Check with your IT department if you have SMTP configured on your network (They even can give you the address of your email server :)).
If SMTP is configured then there is a possibility that you are on a subdomain that doesn’t have a mail exchange record configured. If this is the case then you have to submit email server address in Automation manually. Try to ping it using something like mail.yourdomain or relay.yourdomain. The one that responds most probably would be you mail server.
Please check with your IT department about port number that should be used with your email server. If it’s non-standard (other than 25), then probably it can be it. If you still unable to connect to email server, please send us exact error message(s) you are getting when trying to connect to the server.