Where on docs.platform.sh should be changed?

We need to update the docs for that environmental variable to indicate it is not present in the environment if the setting for email has been disabled for the environment.

What exactly should be updated?

https://docs.platform.sh/development/email.html#5-send-email-from-your-app
and possibly https://docs.platform.sh/development/variables/use-variables.html#use-provided-variables

see context

Additional context

No response