If you have a Gmail account (or Google Apps for Business), you may not be aware that you can embed information in your email address. For example, if your address is:
 
hostseo@gmail.com 
 
You can add arbitrary text like +some_string to the end of the address and make it:
 
hostseo +some_string@gmail.com 
 
Anything after the plus sign is ignored in routing the email, but the additional information can be used for setting up Gmail filters. Filters could be used to perform action like star the message, skip the inbox, or forward to another account.
An example use for aliasing your Gmail account
  
A website such as amazon.com asks for your email address, you can give them an email address like:
 
hostseo +amazon.com@gmail.com 
 
You’ll still get email from them, but also it’s easy to filter messages later on if you need. This is useful for websites that have multiple departments and multiple contact emails (like billing@, info@). And in the rare case if some website loses your email address to a spammer, it may be easier to track down who sold it, or where a security breach may have occurred.
 
For trusted acquaintances, you may give out an email address with some information to protect it from your spam filters.
  
hostseo+somepassword@gmail.com 
 
Or for testing, if you ever need an endless supply of unique email addresses, you can easily create them as:
 
hostseo +test1@gmail.com
hostseo +test2@gmail.com
hostseo +test3@gmail.com 
 
In general, to keep your inbox from becoming unmanageable, maintain some level of separation between emails created by people you know, and emails created by computers/websites.
 
Using aliases in Gmail does not require any additional setup or configuration in Gmail, aside from adding filter rules, if desired. Just append numbers, letters, or any other character that can occur in a valid email username (no spaces, for example) after the “+”.
 
You can always test the alias by sending yourself an email.