When the metoo option is checked, and your email address appears in the To or Cc field when you do a Reply to All, you will receive the reply. Your mail address is recognized in all forms that include your login address, such as yourname@machine and yourname@host. Where machine is the name of your machine and host is the name of any host that is not your machine.
For example, suppose you Reply to All to a message with the following header:
From:salmon@sea Fri Aug 23 10:36:21 1991 To: yourname@machine, yourname@host, tuna@ocean
Your reply will include the following To line:
To: yourname@machine, yourname@host, tuna@ocean, salmon@sea