Dovecot and Stalwart do support push notifications, but are missing some functionality at the moment to make this feature work.

There is a push notification standard called "Internet Message Store Events RFC 5423", the standard defines what events should be accessible and what parameters should be included. BUT the standard does NOT define how the information should be delivered to the consuming service. Therefor there is no standardization on authentication methods or data format (JSON, XML, Other)

Dovecot

Does support the Internet Message Store Events RFC 5423, but does not have built in capabilities to trigger HTTP endpoints on the consuming system. Instead Dovecot uses a plugin structure that triggers methods for each event with the required data according to the RFC. Dovecot does have a pre made plugin that supports Lua scripting which could be used to either directly add changes to the NC database or used to trigger a endpoint on NC.

Pros

• Implements Internet Message Store Events RFC 5423

Cons

• Requires custom plugin/script to transmit notifications

Stalwart

Does have built in capabilities to trigger HTTP endpoints on a consuming system. BUT does not support the Internet Message Store Events RFC 5423 and does not have the ability to use a plugin or scripting to accomplish this. Another issue with Stalwart is the lack of required information in mail operation notification, mainly the accountName (user login or email address) as all operation notification only contain a internal "accountId".

Pros

• Can trigger HTTP endpoints out of the box (JSON)
• Supports all mail operations

Cons

• Does not support RFC required parameters
• Would require revers connections to retrieve required information

Then let's go with Dovecot + Script for now