[multidim]

All services so far seem to accept dots, but the number of possible dot arrangements can be quite limited, and it is a pain to actually use (figure out next one to use, figure out associated service from dot arrangement, etc).

[VectorLock]

Gmail won't let you put anything arbitrary with dots. So if you're [e-mail] you can use [e-mail] but not [e-mail]. Other email system obviously can work however they want.