If you are like me you have probably carelessly subscribed to several mailing lists and you find the regular emails from these merchants to be vaguely annoying. Most of these maliing lists would probably remove you from their mailing list if you took the trouble to follow their process for unsubscribing. However, this can be a lot of trouble and there is always the risk that the senders are unethical hackers and will treat your click on their unsubscribe link as encouragement to send you more annoying emails.
Luckily there is a service called unsubscribe.com which will look after the unsubscription for you. After you register, you can either use their unsubscribe buttons (they have buttons for all of the major public email providers) or else you can simply forward any emails from the mailing list to email@example.com - they have software which can recognize which email list has sent the promotional email to you and they will initiate a removal request on your behalf.
They have a free account which will unregister you from a maximum of 5 lists per week. If you want more you can purchase a paid subscription, but I generally find that 5 per week is enough for me.