system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't emails arrive immediately like Instant Messages? Where does the email go in the time between being sent and being received?
gpt
1. You hit send. Your "client" (phone app, Outlook, web app, whatever) connects to an email _server_. Prior to this your client was just sitting there letting you write the mail.

2. The mail is now sent to _your_ server. Like dropping a letter at the post office box. The server now checks to see where it's going, looks up his way to get there and connects to the other server (the recipient's mail server).

3. Assuming that's all good (it can reach that server), the recipient's server says "ok...I will take that." If something is wrong, it gets denied and either goes into a black hole or informs you or someone else of the problem depending on configuration.

4. The recipient's server now applies a bunch of checks (SPAM and virus filtering) then any rules that the server has to apply then any rules the recipient wants applied.

5. Finally this drops the message wherever it actually belongs which will usually be where you sent it.

6. Here it sits until a client (phone, Outlook, whatever) asks the post office "got anything for me?"


In the case of IM, you are directly connected to a service which is routing the information between users in "real time" because you have both agreed to use the same service to do so, skipping all those other bits.