Re: I've seen a definite uptick in these
Don't try claiming that it's a unique gmail feature.
It was a feature back in the days when email addresses cost money, some people wanted more than one address, and neither security nor spam were issues.
It was a minor feature of my mail-by-web software from 1997. Back when webmail and other web-based office facilities like docs and calendars looked like a cool new thing people would find useful.