The least complexity in the opt-out is a mailing system official service mailbox. Such letters come to the boxes located on free email hosting: mail, rambler, yandex, etc. Therefore, if your mailing list comes from an official source, the most simple solution is to go to the settings box and click "unsubscribe from all mailings".
It is not difficult to unsubscribe from newsletters, if they come from official news and other mass portals. In General, any site that is well-proven (according to user reviews). To unsubscribe from the mailing list, the source of which are such sites that need: it is necessary to open the letter sent with the mailing of the website and view it. Usually at the bottom there is the inscription "unsubscribe". Simply click on the item and then confirm your decision.
Sometimes the newsletter comes from the website where you registered, but at the bottom of the letter there is no point to "unsubscribe", then you need to go to the website and search for contacts to contact. Usually contacts administration says in a special section "contacts", "communication" or a similar name. As soon as you find a means of communication, write a letter with a request that we stop sending the newsletter.
If the problem is not solved, i.e., you write a letter to the administration, but there is no response, or sending coming from unknown source, then it is possible that it was spam. It is necessary to block separately. Some mail systems have a button "this is spam" it should be to choose the opposite letter. If such feature is not on your mailbox, the e-mail sender should be put in the "black list". In order to avoid such troubles, should not be spread in open access personal e-mail. Or, at least, to use simple security tools (e.g., http://2ip.ru/spambot).