[pwg]

UUCP delivered email (and Usenet and file transfers) for a very long time before full time network connections became the norm.

https://en.wikipedia.org/wiki/UUCP

So, it is possible to send/receive email without an always on network connection.

[jrochkind1]

Heck, you could even do it with a never-on network connection, if someone wants to periodically ferry the ingoing/outgoing email over on a drive.

That probably isn't what the requirements makers had in mind though.

[mikeash]

I can see it now. You spend a month implementing a fancy, modern store-and-forward system that ticks all the boxes and provides an excellent blend of security and functionality. Then you get called into the big shot's office because he wants emails to go through in under ten seconds.