Suddenly not receiving any store emails

We are suddenly not receiving any emails through zencart. When some uses the contact us form, no email is ever received. When someone places an order no email confirmation is received. We use the Ceon payment module that sends the middle credit card digits in a separate email. That email never comes as well. In ZenCart, if I try using the send message feature and sending an email to our email address, it does not come through. If I try a different email address it goes through just fine. If I go to the Ceon Payment module and change the email address there, then the credit card info will send to that address just fine when I place an order. However I can not get anything to send to our regular email address. It has worked fine for years, and no changes have been made in ZenCart recently. Is this a configuration problem in ZenCart, or perhaps an issue with my email provider? The emails are just non existent.

Here is some of the server info, would be happy to provide anything else needed:
PHP Version: 5.2.17 (Zend: 2.2.0) PHP Memory Limit: 256M
Database: MySQL 5.5.42-37.1

What is your "regular" email
What is the email that works?

Our regular email goes through zianet. The other email I tried experimenting with was gmail.

If you are not using SMTPAUTH try switching to it and use these settings

SMTP Email Account Mailbox 	[email protected] 
SMTP Email Account Password 	******* 
SMTP Email Mail Host 	mail.zianet.com
SMTP Email Mail Server Port 	587

http://w3.zianet.com/email-setup/17-support.html

Thanks, I switched to SMTPAUTH and applied those setting with the right credentials, however when I try to send a message I get the "Email Error: SMTP Error: Could not connect to SMTP host." error.

Before trying that I was running PHP.

I would kick this up to zianet
Those settings are straight from their site

Thanks for the help, it does indeed to be a problem with my hosting site and my e-mail server communicating.