Much Less Than An Unlimited Number
There you will read: "By default, an SMTP virtual server can accept virtually an unlimited number of incoming network connections (although the actual physical limit is much less than this)."
Huh? What number is much less than virtually unlimited? That is like saying: "I'll give you much less than an infinite amount of money."
Turns out that "much less than unlimited" used to be 2000, but now is the default of 5000.