Xcode server bot can’t send emails using sendmail

I’ve been trying for weeks to get Xcode Server Bots to send emails after an Integration. I’ve narrowed it down to these logs:

kernel    Sandbox: sendmail(48548) deny(1) forbidden-exec-sugid
sendmail    fatal: execvp /usr/sbin/postdrop: Operation not permitted
sendmail    warning: command "/usr/sbin/postdrop -r" exited with status 1
sendmail    fatal: xcode@<redacted>.com(450): unable to execute /usr/sbin/postdrop -r: Undefined error: 0

It seems there might be a permission issue as it’s the Sandbox complaining.

My postdrop permissions seem to be correct compared to what I can find online:

-rwxr-xr-x    1 root   wheel        570448  1 Jan  2020 postalias
-rwxr-xr-x    1 root   wheel        466416  1 Jan  2020 postcat
-rwxr-xr-x    1 root   wheel        823488  1 Jan  2020 postconf
-rwxr-sr-x    1 root   _postdrop    588624  1 Jan  2020 postdrop
-rwxr-xr-x    1 root   wheel        431904  1 Jan  2020 postfix
-rwxr-xr-x    1 root   wheel        432032  1 Jan  2020 postkick
-rwxr-xr-x    1 root   wheel        449424  1 Jan  2020 postlock
-rwxr-xr-x    1 root   wheel        431872  1 Jan  2020 postlog
-rwxr-xr-x    1 root   wheel        569632  1 Jan  2020 postmap
-rwxr-xr-x    1 root   wheel        465872  1 Jan  2020 postmulti
-rwxr-sr-x    1 root   _postdrop    588448  1 Jan  2020 postqueue
-rwxr-xr-x    1 root   wheel        466784  1 Jan  2020 postsuper

I have followed many tutorials to get this working and have everything setup as they say. I can successfully send email from the command line, but this seems to be a user permission issue from the XCSIntegrationService.