It kinda bugs me when people describe +foo as a "gmail trick". That type of addressing predates gmail, and exists outside of it still. In fact the plus is not

It kinda bugs me when people describe +foo as a "gmail trick". That type of addressing predates gmail, and exists outside of it still. In fact the plus is not the only form of this. qmail uses the dash, and postfix allows you to configure anything as a separator.