Email is being delivered to the wrong person with a similar gmail address

Gmail allows you to use periods in your email address but ignores them.   Gmail treats two similar email addresses the same when the only variance is a period, which is why the email you are sending out could be delivered to the wrong person if their address is similar with the exception of periods.  Below is an article that talks about it and you can find other references if you google it.

https://gmail.googleblog.com/2008/03/2-hidden-ways-to-get-more-from-your.html