Thanks @supermathie
My app.yml now reads:
env:
LANG: en_US.UTF-8
# DISCOURSE_DEFAULT_LOCALE: en
## How many concurrent web requests are supported? Depends on memory and CPU cores.
## will be set automatically by bootstrap based on detected CPUs, or you can override
UNICORN_WORKERS: 8
## Added this line on 04/10/25
## REF: https://meta.discourse.org/t/is-there-a-way-i-can-send-email-notifications-faster/383103/12
DISCOURSE_SIDEKIQ_WORKERS: 7
I’ll rebuild later in the week and time it sending emails 
Just so I know my change has taken effect, am I right in thinking this Threads value should increase from 5 to 7?
