Stop cron daemon “symmetrical.xm” error messages in Terminal mail

After upgrading to High Sierra (I think) I've started receiving the following message almost every time I start up Terminal:

You have new mail in /var/mail/MyUsername

I had some problems upgrading to High Sierra so I strongly suspect this started after the upgrade, but cannot be absolutely certain.

When I enter the $ mail command and read the messages (which can amount to hundreds at one go) this is what is written:

Message 1:
From MyUsername@Users-MacBook-Pro.local  Tue Nov 28 21:37:04 2017
X-Original-To: MyUsername
Delivered-To: MyUsername@Users-MacBook-Pro.local
From: MyUsername@Users-MacBook-Pro.local (Cron Daemon)
To: MyUsername@Users-MacBook-Pro.local
Subject: Cron <MyUsername@Users-MacBook-Pro> /Users/MyUsername/Library/symmetrical.xm/symmetrical.xm cr
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=MyUsername>
X-Cron-Env: <USER=MyUsername>
X-Cron-Env: <HOME=/Users/MyUsername>
Date: Tue, 28 Nov 2017 21:37:01 +0800 (+08)

/bin/sh: /Users/MyUsername/Library/symmetrical.xm/symmetrical.xm: No such file or directory

Also, when I run $ crontab -e, this is what is returned:

37 * * * * /Users/MyUsername/Library/symmetrical.xm/symmetrical.xm cr
~                                                                                                                              
~                                                                                                                             
"/tmp/crontab.SsevmMDt1o" 1L, 72C

I am trying to figure out why the Cron Daemon is sending me these error messages. To clarify, I would not like to suppress mail from cron altogether; so, I don't want to

• Delete the MyUsername file at /var/mail/, OR
• Change the MAILTO variable in /etc/crontab to MAILTO="" (as suggested in this link)

Instead, I'd be really grateful it if someone could help me understand

• How/why this started happening
• What I can do to stop it from happening again (or if I should stop it from happening at all)
• Which app/script requires the missing file/directory called symmetrical.xm and why

Any other additional information to add to the points listed above would also be greatly appreciated.

Thank you!

macOS High Sierra v10.13.1 (17B48)