com.apple.postfix.master Service exited with abnormal code: 1

My group manages about 100 sites, and sometimes I schedule things on a server root's crontab that I would like an email from the server with output from the command(s) I scheduled. This works great on some sites -- just set the MAILTO= to my email address. But there are other sites where I don't get emails, and I find the following in the system.log at the time the email should be sending:

Nov 18 09:11:06 xxhostnamexx com.apple.xpc.launchd[1] (com.apple.postfix.master[34981]): Service exited with abnormal code: 1

Nov 18 09:11:06 xxhostnamexx com.apple.xpc.launchd[1] (com.apple.postfix.master): Service only ran for 2 seconds. Pushing respawn out by 8 seconds.

Nov 18 09:11:16 xxhostnamexx com.apple.xpc.launchd[1] (com.apple.postfix.master[34981]): Service exited with abnormal code: 1

This is pretty cryptic! (I do find it intriguing that the process ID number in the second error is higher than the first. So, yes, it tries, crashes, tries again, then gives up.) The server that I'm looking at today is running 10.12.3, but I have the same problem with a smattering of other servers and they are running various OS versions.

So does anybody have any clues as to why I can't get the mailer to run for more that 2 seconds on some servers, while it runs just fine on others?