Comment by canucker2016

I wouldn't call either Mail Pump's slow email processing a "benevolent deception", nor Exchange's quick email processing an attempt to be perceived as a fast email server.

In MSMail/Exchange Client/Outlook, the presence of email in the Outbox folder signifies that an email is to be sent, but that the code for sending the email hasn't processed that particular email.

MSMail being slower than Exchange to send email is a leaky abstraction due to software architecture.

Win3.x doesn't support multithreaded apps, using a cooperative multitasking system. Any app doing real work would prevent the user from accessing the system since no user interface events would be processed.

So the Mail Pump would check to see if the system was idle. There are no public or secret/private Windows APIs (despite all the MS detractors) for code to determine if the system is idle - you, the developer, had to fall back to using heuristics. These heuristics aren't fast - you didn't want to declare that the system was idle only to discover the user was in the middle of an operation. So the Mail Pump had to be patient. That meant the email could sit in the outbox for more than a second.

Exchange Server was a server process running on a separate box. When an email client notified the Exchange Server that an email was to be sent (whether via RPC or SMTP command), Exchange Server didn't have to wait in case it would block the user's interaction with the computer. Exchange Server could process the email almost immediately.

But there was a happy resolution to the conundrum - no, the Exchange Server didn't add a delay.

Some architect/program manager had added a "delay before sending/processing" property to the list of supported properties of an email message. The Exchange/Win95/Capone email client didn't use/set this property. But a developer could write an email extension, allow the user to specify a default delay for each outgoing email and the extension could get notified when an email was sent and set this "delay before sending/processing" property, such that Exchange Server would wait at least the specified delay time before processing the email message.

The user who desired an extended delay before their sent email was processed by the Exchange Server, could install this client extension, and specify a desired delay interval.

Outlook eventually added support for this property a few years later.

I notice that Gmail has added support for a delay to enable the user to undo sent emails.