Problem with sending email

While I mail invoice to customers the following message appears

System.ArgumentException: System.ArgumentException: This property cannot be set to an empty string.
Parameter name: value
at System.Net.Mail.SmtpClient.set_Host(String value)
at ManagerServer.HttpHandlers.Businesses.Business.Email.Post()

Please resolve the issue

You probably have not set all the values needed.

Go to [Settings] [Email settings] and see if your emaildata is ok, for instance:

I had the same issue. It was from the theme.