[prash_ant]

Yes, but the fraction of users using the +company part would be similar to the fraction of linux desktop users on the internet.

The way we don't see most software companies supporting linux desktop users simply because it is not profitable, we can hypothesize that the spammers won't spend time-energy-money on getting the +company filtered out.

[remram]

This is common enough that many sign-up forms reject the +. Spammers can definitely do that much.