Hello
I know this post is over a year old.
We're switching SmarterMail to Linux soon, and I'm also wondering whether it's okay to run Rspamd and SmarterMail on the same server.
Looking at the system load Rspamd causes, it's harmless. SmarterMail is actually quite resource-efficient.
Our server processes fewer than 10,000 emails per day. The cloud server for Rspamd runs with 2 CPUs and 4 GB of RAM, while SmarterMail runs with 4 CPUs and 8 GB of RAM. Both servers are rather boring :-)
Regarding maintenance: This definitely saves time and downtime. A system update only runs once. Updating the Linux version of SmarterMail is also lightning fast.
I see no reason why SmarterMail and Rspamd can't be run on the same server.