mail: cannot send message: Process exited with a non-zero status

[Moses Moore]

Steps to reproduce:
 - install postfix (any MTA?) for local mail only, and mailutils for `/usr/bin/mail`
 - install integrit, default config
 - run it once to set the "known" values
 - `apt get upgrade`
 - launch `/etc/cron.daily/integrit`

Expect to see:
 - large email with all the changes

What I saw instead:
 - ```
   /etc/cron.daily/integrit:
   mail: cannot send message: Process exited with a non-zero status
   run-parts: /etc/cron.daily/integrit exited with return code 1
   ```

Also seen:
 - in /var/log/mail.err
   "postfix/sendmail[]: fatal: root@thismachine(0): message file too big
 - adding `stat -c %s "$REPORT"` to the cronjob it says the $REPORT file size is 12MB

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: integrit 4.1-1.1 [modified: etc/cron.daily/integrit]
ProcVersionSignature: Ubuntu 5.15.0-70.77-generic 5.15.92
Uname: Linux 5.15.0-70-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.4
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Sun Apr 30 15:01:07 2023
ProcEnviron:
 TERM=screen-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: integrit
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.cron.daily.integrit: [modified]
modified.conffile..etc.integrit.integrit.conf: [inaccessible: [Errno 13] Permission denied: '/etc/integrit/integrit.conf']
modified.conffile..etc.integrit.integrit.debian.conf: [inaccessible: [Errno 13] Permission denied: '/etc/integrit/integrit.debian.conf']
mtime.conffile..etc.cron.daily.integrit: 2023-04-30T15:00:46.103883

[Moses Moore (moses-ubuntu)]

What I did in the meantime:
- see if the report tempfile is still in /var/lib/integrit
- cd /var/lib/integrit ; mv {current,known}.cdb # and pray to the divine for protection
- add this before the 'mail' line at the bottom of /etc/cron.daily/integrit:
  ```
  reportsize=$(stat -c %s "$REPORT")
  if [ $reportsize -gt 8388608 ]; then
      echo >&2 "$REPORT is $((reportsize / 1048576))MB email may not send"
  fi
  ```