Usually situated outside the cloud. However, since it's limited in its ability to queue messages at the receiving end, it's usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server. You send e-mail with SMTP and a mail handler receives it on your recipient's behalf. Internet Protocol is the method or protocol by which data is sent from one computer to another on the Internet. Each of these packets contains both the sender's Internet address and the receiver's address.
Any packet is sent first to a gateway computer that understands a small part of the Internet.
The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognises the packet as belonging to a computer within its immediate neighbourhood or domain. That gateway then forwards the packet directly to the computer whose address is specified. Although each packet has the same destination IP address, it may get routed differently through the network. X.400 is common in Europe and Canada. It's actually a set of standards, each in the 400-number range.