hi Mate, an internal user received this msg, with 2 MS office webpages opens only
Documentation says it is for revoked certificate list.
Should I add a safe rule for antivirus?
Thanks in advice
Welcome to the Let's Encrypt Community, @MyselfA! 
I have notified the staff of this issue. Please be patient and give them a chance to respond.
We occasionally get antivirus systems classifiying our URLs as malicious because they saw malware connecting to them, but that is a false alarm. I will submit a complaint to ESET.
Why my clients are connecting to lencr.org ?
I guess I used it once along with CertBot on a internal linux server.
Its that the reason?
Please see:
Look at this
https://letsencrypt.org/docs/lencr.org/