Password emails and personal messages for example, need to be delivered immediately, while newsletter emails can be drip fed over a long period. Currently all emails fall in the same queue, if the mail server has a queue.
Is it possible to have two separate smtp server settings defined to route both types of mails with different priorities?
Thanks.
You could need a plugin. It will not be easy.
If you really want to do that, I think your best bet would be to create your own mail server that accepted all the mail, determined if it was important or not, and then treated it accordingly.
Thanks. I use postfix with a queue right now.
I don’t think it offers prioritization of emails now or that it is going to be easy to do it.
I have no idea how to do it with postfix, but if you were going to pay me money to solve the problem, I’d start on the postfix side, not the discourse side. (I am not asking for money to solve the problem; it’s the kind of job that I’d set an obscenely high
rate for and then be sorry when the client accepted the bid! 
)
No, this has been asked before, dual SMTP is not in the cards.
Con las notificaciones de chat que ahora se suman a los correos electrónicos que deben entregarse rápidamente, investigué un poco más y tengo una buena configuración de trabajo. Aquí hay algunos consejos para cualquiera que necesite esto.
Postfix ofrece verificaciones de encabezado para filtrar y reenviar mensajes a través de diferentes servidores smtp. Por lo tanto, todo lo que necesita son dos servidores smtp para correos electrónicos normales y prioritarios; y ediciones a tres archivos de configuración de postfix.