Turns out that gmail, outlook, and yahoo all support this little trick:
All you need to do, is to add something to the end of existing email address – and voila! You can have unlimited number of test emails.
So, someemail@gmail.com can be easily turned into someemail+testtest@gmail.com
Same result, but a unique email address.
Also, dots seem to have no effect on delivery of email. So for example: s.o.m.e.e.m.a.i.l@gmail.com will be happily delivered to correct addressee.
http://www.plankdesign.com/blog/2013/06/testing-infinite-unique-email-addresses-with-gmail/