I've found that a lot of websites don't like "+" or even intentionally detect it to reject it or subvert the user's interest. I think a good system would be a

I've found that a lot of websites don't like "+" or even intentionally detect it to reject it or subvert the user's interest. I think a good system would be a randomly generated handle like nick836742@example.com where my real email probably isn't nick@example.com, but the number is different for each service.