If you have not been receiving Form mail, registration, or subscription notifications from your WordPress site, and Godaddy is your web host provider, it may be due to some recent changes or rather policy implementations made by Godaddy.

WordPress mail notifications are sent using native PHP mail().  This is the same no matter which subscription or form plugins you are using like CForms II or Subscribe2, any forum or other mail handling plugins.  Some provide the option to use separate PHP or SMTP mail handing scripts, but most rely on the native WordPress registration email.  Per Godaddy:

If you use the mail() function in your PHP, you do not need to specify an outgoing mail server. If you are using some other method besides mail() in your PHP code, use relay-hosting.secureserver.net for your relay server.

NOTE: A maximum of 1000 emails per day are allowed through our relay servers.

AND MOST IMPORTANTLY:

Our mail server will not send email containing a “From:” header entry of aol, gmail, yahoo, hotmail, live, aim, or msn.

So if your WordPress administrative email account is setup under one of these mail providers, you have 2 options to ensure you receive mail from and are able to send mail to visitors.

A.  Change your WordPress Administrative email to name@yourdomain.com.  Godaddy typically offers a free 1G email account with hosting.  Don’t forget to change the FROM:  line in any Form or subscription settings you have.

B.  If you have multiple WordPress accounts you manage under your current email, and don’t want to change the WP administrative email, you can use a plugin like WP-Mail-SMTP to either configure SMTP mail or to change the FROM: email to another supported domain like yourdomain.com.  If you prefer to use gmail, or another you check regularly, I recommend doing the following:

1. From godaddy, create an email account on your domain.  Set up CC: to send to your preferred email as well. 
2. Install the WP-Mail-SMTP  plugin and activate it.
3. Settings -> Email.  From Email:  yourgodaddyemail@yourdomain.com.
4. From Name:  The name you want to use.
5. Mailer:  Use the PHP mail() function to send emails.
6. SMTP Host:  relay-hosting.secureserver.net
7. SMTP Port: 25
8. Encryption:  No Encryption
9. Authentication:  Yes, Use SMTP Authentication
10. Username: yourgodaddyemail@yourdomain.com
11. Password:  Your godaddy email password
12. Update
13. Update your new FROM: email address in any forms, subscriptions, forum, etc plugin settings
14. Test