MacOS does not trust Let's Encrypt certificate after renew

My iMac Pro 2018 does not trust Let's Encrypt certificate every 90days after it self renew, there is no setting for me to trust the certificate on my iMac Pro. It does not happen to my other iMac Pro 2015 in an non-restricted internet access environment.
I am using Synology NAS, version: DSM 7.1-42661 Update 4 in a restricted internet access environment.

Might I know is there any firewall link I can add to prevent macOS's Let's Encrypt certificate to be trusted?

Whatever is going on, it assuredly has nothing to do with any firewall. Unfortunately, you've given us no information to go on to determine what it is. But let's start with this: exactly which application is giving you an error, and exactly what error is it giving you?


Face the problem when users are using Apple mail

Sadly I do not have any screenshot, in the application it will prompt certificate is not trusted,

If other devices automatically trust that cert, then the cert isn't the problem.
Your system is then likely unable to trust it because it has an outdated trust store.

This is not a MacOS forum, but you might be able to search solutions to similar problems.


Without an URL (IMAP, POP3, HTTPS, depending on the service used) and/or clear error message, there is little sane to say about this unfortunately.


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