When I register an email address for a website, I normally create a new email alias unique to that website or the company associated with the website. Unfortuately, many companies and websites sell their email lists to other companies, ususally labelled as their "partners" in their privacy policies, seeing that as a way to make additional revenue from their customers or website visitors. Even if a company states they won't do so, most reserve the right to change their privacy policy at any time and there is also the possibility that the company will go out of business at some point and all assets, including its mailing lists, will be sold to others.
I receive an inordinate amount of spam every day and waste a lot of time purging it from my inbox, so by creating an email alias, which I can easily do, since I manage the email server that processes my email, I can simply invalidate any alias when I notice I'm receiving a lot of spam with a particular alias I created in the "to" field. E.g., if I created an alias Acme_2014@example.com that points to Me@example.com and start receiving spam to Acme_2014@example.com, I know that the Acme Corporation sold my email address to a spammer or had a compromise of their server holding my account information.
Since Acme_2014 is not an email address that a spammer who employs name dictionaries to distribute spam might use, I can be sure that the source of the email is using the email address I gave to the Acme Corporation. If I used an address such as abe, bill, or zachary@example.com, I couldn't be certain, since some spammers try sending email to a domain using every name from a name dictionary. I also wouldn't use acme@example.com, since that is a word in an English language dictionary, so spammers using a dictionary for building email addresses might use it.
I can easily create aliases on my email server, but there are a number of online services that will allow you to create such aliases to thwart spammers. E.g., with such a service you might be able to create an alias acme_2014@spamblock1.com that points to me@example.com, if me@example.com is the email address you normally use.
If you wanted to communicate with Acme Corporation by email, you might need to use the alias you used in the "from" field of email you send to them. To do so in Thunderbird 24.2.0, right-click on your account, which should be located at the top of the left pane of the Thunderbird window. E.g., you may see me@example.com there. Select Settings, then put the alias in the Email Address field and, if needed, set the Your Name field appropriately, then click on OK. Once you have sent the email you needed to send to the Acme Corporation you can change the settings back to those you normally use.
