Most spammers know about that trick, and their software automatically strips the + and anything after it. Their software has been doing that for about 20 years already, sadly. The + trick really only works with people you trust already. Also, + addressing is in the RFC, so pretty much every mail server supports it.

Gmail also added . (dot) as a non-counted character, so you can put as many of those as you want into the user field, but most spam software is catching onto that too.