No new certificate (Let's Encrypt) for my mail server

[cfusco]

Reverse Path Filtering prevents certbot renewal using HTTP-1 acme-challenge

Found it: sysctl net.ipv4.conf.default.rp_filter=2 sysctl net.ipv4.conf.all.rp_filter=2 As I suspected, with these two commands, let’s encrypt now works. I will report the problem to their forum and see If I can do something about it.