Subscribe by email is not working.

We cannot get the subscription emails to work. Our tech guys think that "Gmail is bouncing the email as it is being generated in a non-compliance method. Emails generated from automated scripts sometimes lack the usual headers of a standard email which is detected by Gmail as 'spam' hence rejected. There is a configuration of email format in the plugin which may need to be changed."

Is this the case? Is there any other reason why our emails are not being received by external mail servers?