MAPI does not perform the deferred delivery; it is an option of the underlying messaging system to handle deferred delivery.
you would have to find out which "messaging system" is used by Outlook
and if that is also used by Net.Mail
. But I guess it is related to Outlook
only: So how does this ‘Deferred Delivery’ thing work? – You Had Me At EHLO…
The RFC 4021: 2.1.65. Header Field: Deferred-Delivery
] is mainly of informational purpose. The standards allow gateways to delay mails having this field but you should not rely on that.
You can implement it in your application using a timer when your application is not terminated while having queued mails. Or you can start your application using a scheduler and let it check for mails to be send.