A CGI script searches for email address records that match a provided search term.
I scrape addresses from email I've archived for a couple of decades. I find this handy when looking up old friends and colleagues.
I've had various computer systems that try to do this for me but they make finding emails harder or aren't supported for as long as I want to keep emails. Better to have my own.
I write scraped addresses to a file, one email per line, with a list of years where I've seen it used. I rebuild this with a nightly cron job. I search this with grep built into a cgi script on the machine where I keep my mail.