We are utilizing Odoo 17 and an external email server with a sending limit of 200 emails per hour

Hi Massimo, 

1. What version of Odoo are you on - Odoo Online, SH, or On-premise? 
2. Have you setup your own Outgoing Email Server setup?

Asking because there is a daily limit on Odoo database if you're not using your own Outgoing Email Servers. Also, 200 every hour could do a lot of reputation damage to your domain.

Thanks for the confirmation, Massimo.

It should be possible via System Parameters. But, since Odoo chose not to reveal all the Keys associated with a particular model, it's hard to determine the right Key for this job. For instance, we can deduce the model to be mass_mailing but the Key is the unknown (for me, at least). Because, it could be mass_mailing.batch_size or​ mass_mailing.batch_limit​. Same story with the interval, it could be mass_mailing.batch_interval or mass_mailing.queue_interval​. 

Sorry, I understand this isn't very helpful. Let's see if someone else contributes to this thread.