On 1 Oct 2018, at 3:56, James Brown wrote:
Is this a SIP thing?
Yes. As Viktor said, Apple-populated paths under /usr are immutable while SIP is enabled.
Anyone come across this? How to fix?
Don't fight it. As Viktor said, you can adjust your build to NOT replace the system 'sendmail' (which is Apple's custom-built Postfix 3.2.2.) Even if you disable SIP to do that replacement, you will not be informed when a future minor system update re-installs Apple's binary.
If you don't feel like cobbling up your own build under the Homebrew model, MacPorts has a mature flexible port for Postfix, along with all of its dependencies and possible dependencies (e.g. Dovecot, if you're using it's SASL layer.)
And of course you CAN just try to work with Apple's build and buy their additions (not sure what those are exactly any more...) at the cost of their compile-time config choices. Everything you need to configure it is right there in /etc/postfix/...
