Something like spamgourmet.

WHY THIS EXISTS

Having a public email address is an invitation to spam. Private email addresses allow you to filter your spam based on how much you receive and from whom it came. Instead of giving your main email address to every web site you run across, you can give a private email address to each web site (e.g., "facebook@myspam.example.com" for Facebook). That way if you no longer want to receive email from a given sender, you can easily filter it out.

Additionally, by having site-specific email addresses you can also tell when a breach of security happened. If I tell Home Depot my email address is home-depot@myspam.example.com and I start receiving spam from Nigeria on that address I know that Home Depot has had a security breach. I can use that to inform Home Depot, Twitter, my friends that there's been a breach, in addition to checking credit cards for possible fraudulent charges.

In short, having private email addresses per organization allows you to keep tabs on your private life and help keep you more secure.

It would be remiss to not mention spamgourmet.com, a wonderful service that was the inspiration for this code. I've been a happy spamgourmet user for many years, but unfortunately it has some problems this software attempts to address:

spamgourmet.com and its various addresses are too well known. By hosting this on your own domain you can prevent, for instance, Facebook from filtering your email address.
spamgourmet addresses are very long and hard to communicate over the phone or when filling out forms at, say, a doctor's office. This is attempting to provide much shorter addresses that will raise fewer eyebrows and can be communicated more easily.

HOW IT WORKS

Once the software is installed (see INSTALLATION, below), it will start receiving all email directed at it (such as by procmail or sieve), and it will examine the destination address (i.e., "To" header) to determine whether it should deliver the email to the final recipient or not.

SpamCat relies on your MTA delivering mail from your spam domain to a real email address that can be used for IMAP/POP/etc. This can be accomplished in any number of ways based on your MTA/LMTP/LDA setup; an example for Postfix/Dovecot is below.

When SpamCat receives a message it looks at the username (the left-hand of the "@" in an email address) to determine the sender. Thus, "foo@bar.com"'s sender is "foo".

Once the sender is determined SpamCat will see how many messages are remaining for that sender, and if the sender has no remaining messages then the message is thrown away.

If the sender has messages remaining then the message is delivered as-is with the exception that the Subject header shows how many messages are remaining and the total number of messages available (e.g., "Subject: XANAX FOR NIGERIA - [19/20]" shows that there are 20 total messages from this sender, and there are 19 remaining).

RECOMMENDED USAGE

Create your own spam-handling domain (e.g., "spam.example.com")
Use private email addresses in that domain anywhere you're asked for an email address (e.g., giving ShopRite an address of "shoprite@spam.example.com")

PREREQUISITES

Perl 5
Email::Simple
SQLite 3
DBD::SQLite

INSTALLATION

See INSTALL to install the library and spamcat executable.
Once the spamcat executable is installed you'll need to add it to your procmail, sieve, or some other similar device that writes email to standard input and receives the transformed email on standard output.
You will also need to create a config file for spamcat (see config/spamcat.conf for an example) somewhere that can be read by spamcat.
Make sure you pass in the spamcat.conf file to spamcat via the "-c" argument (e.g., "spamcat -c /home/me/etc/spamcat.conf").

EXAMPLES

Postfix

main.cf

Postfix needs to know that the spam domain should be handled locally.

Virtual_mailbox_domains = spamcat.domain somewhere.else

virtual aliases table

Make sure postfix can route the spam domain to the user who should receive it.

@spamcat.domain  hidden-address@somewhere.else

Dovecot/Sieve

The sieve file for the user which receives mail for the spam domain should pipe the email into spamcat, which will handle final delivery for the spam domain.

require ["fileinto", "envelope", "vnd.dovecot.filter"];

if address :contains "to" "@spamcat.domain" {
  filter "spamcat" ["-c", "/path/to/spamcat.conf"];
}

DNS

The MX record for your spam domain should point to the MTA that hosts spamcat.

spamcat.domain MX 10 yourmta.domain.