How retrieve database data from email?

Hello People: I have my pages built in PHP / Mysql, all working ok, but now I need solve a problem I don't know how to solve or even how search about. Case this problem was already discussed in this list, I would be grateful if someone pass to me correct date so I can search about. My problem is very simple: I have customers who dont want enter into html pages to retrieve some info (suppose info are stock values), but rather they want to send email with formatted query into mail subject (or at least in body) , and then receive response again by email. For instance, customer could send this for stocks@alpha.com to: stocks@alpha.com subject: name=ibm, year=2001 body: (empty) In response, he should receive an email with all IBM stock prices day by day. That't all, I hope this will have solution, but I can't figure how email could communicate automatically with PHP/Mysql. Thanks Miguel