Hi,
You can set the action for the Submit button as Rules and Custom code and paste the following in the Submit_clicked event.
System.Text.StringBuilder message = new System.Text.StringBuilder();
message.AppendLine("Your Mail content here");
System.Collections.Specialized.StringDictionary messageHeader = new System.Collections.Specialized.StringDictionary();
messageHeader.Add("to", "ToEmail");
messageHeader.Add("from", "FromEmail");
messageHeader.Add("subject", "Subject");
messageHeader.Add("content-type", "text/plain");
Microsoft.SharePoint.Utilities.SPUtility.SendEmail(
SPContext.Current.Web, messageHeader, message.ToString());
This will send your email regardless of the other submit actions.