I am building a basic support request system where the customer can log in and ask a question and an admin can go in and reply and it will set the status to \"Responded\" an
If you want their reply to be automatically inserted into the DB, you'll have a assign a cron job in your server to run a php script to detect whether there's a reply from a customer (you need a table listing the customers' email and names.
Each time a customer uses the ticket system their email and name goes into this table).
You'll need to connect to your Inbox too via imap or SMTP, and there are scripts to do this (phpmailer, swiftmailer, etc) and "walk" through each email and see if the sender email matches any in your customers table. Then so an INSERT to the comments table.
Anther way is to read through the emails each time the comments page is loaded, but this will cause the page to take longer to load. However, the data will always be more "real-time" compared to cron jobs.
When sending the email to the user you can have it sent from an email address created for that specific ticket. Something that can identify it with your email system to help you route it back to the php ticketing system.
support(ticketnumber)@domain
support12345@mydomain.com
Then it depends on your email server how to go from there. There are several useful tips at this question that may help or get your started.
How to get email and their attachments from PHP
You could use email piping (if your server supports it).
In the subject, you'd have a unique identifier which contains the ticket ID or something unique to the ticket. Example: "How do I eat food [Question: #1234]", where 1234 is the ticket ID.
In your control panel, you would set up an email forwarder to your email piping script.
This tutorial offers the basics to email piping, and I used it as the base for my piping script: http://www.damnsemicolon.com/php/parse-emails-in-php-with-email-piping-part-1