==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.3.1
- Deployed with iRedMail Easy or the downloadable installer? Downloadable
- Linux/BSD distribution name and version: CentOS Linux release 7.8.2003 (Core)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL/MariaDB
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

My Let's Encrypt SSL cert renewal cron appears to be working, just had the first renewal at the (expires in 30 days point) last week.
I noticed in the daily email that the service restart command exited with an error and have been unable to determine how to fix it.

# Let's Encrypt SSL certificate renewal
38 21 * * * certbot renew --post-hook 'service postfix restart; service nginx restart; service dovecot restart'

running the command [service postfix status] shows all 3 restarted pretty close to the same time and matches the log below.

#log
2020-07-22 21:42:26,756:DEBUG:acme.client:Storing nonce:
2020-07-22 21:42:26,758:DEBUG:certbot._internal.storage:Writing new private key to /etc/letsencrypt/archive/[domain]/privkey2.pem.
2020-07-22 21:42:26,758:DEBUG:certbot._internal.storage:Writing certificate to /etc/letsencrypt/archive/[domain]/cert2.pem.
2020-07-22 21:42:26,759:DEBUG:certbot._internal.storage:Writing chain to /etc/letsencrypt/archive/[domain]/chain2.pem.
2020-07-22 21:42:26,759:DEBUG:certbot._internal.storage:Writing full chain to /etc/letsencrypt/archive/[domain]/fullchain2.pem.
2020-07-22 21:42:26,766:DEBUG:certbot._internal.cli:Var post_hook=service postfix restart; service nginx restart; service dovecot restart (set by user).
2020-07-22 21:42:26,768:DEBUG:certbot._internal.storage:Writing new config /etc/letsencrypt/renewal/[domain].conf.new.
2020-07-22 21:42:26,772:DEBUG:certbot._internal.plugins.selection:Requested authenticator webroot and installer None
2020-07-22 21:42:26,773:DEBUG:certbot._internal.renewal:no renewal failures
2020-07-22 21:42:26,773:INFO:certbot._internal.hooks:Running post-hook command: service postfix restart; service nginx restart; service dovecot restart
2020-07-22 21:42:33,088:ERROR:certbot._internal.hooks:Error output from post-hook command service:
Redirecting to /bin/systemctl restart postfix.service
Redirecting to /bin/systemctl restart nginx.service
Redirecting to /bin/systemctl restart dovecot.service

#Email message
Saving debug log to /var/log/letsencrypt/letsencrypt.log

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Processing /etc/letsencrypt/renewal/[domain].conf
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Cert is due for renewal, auto-renewing...
Non-interactive renewal: random delay of 257.566080286 seconds
Plugins selected: Authenticator web-root, Installer None
Starting new HTTPS connection (1): acme-v02.api.letsencrypt.org
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for [domain]
Using the webroot path /var/www/html for all unmatched domains.
Waiting for verification...
Cleaning up challenges

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new certificate deployed without reload, fullchain is
/etc/letsencrypt/live/[domain]/fullchain.pem
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Congratulations, all renewals succeeded. The following certs have been renewed:
  /etc/letsencrypt/live/[domain]/fullchain.pem (success)
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Running post-hook command: service postfix restart; service nginx restart; service dovecot restart
Error output from post-hook command service:
Redirecting to /bin/systemctl restart postfix.service
Redirecting to /bin/systemctl restart nginx.service
Redirecting to /bin/systemctl restart dovecot.service