[Rspamd-Users] Certificate error with maps.rspamd.com

[Kai Schaetzl]

For some time now my server gets an error when contacting maps.spamd.com: 
error reading https://maps.rspamd.com/freemail/disposable.txt.zst
(88.198.198.21:443): connection with http server terminated incorrectly: 
ssl connect error: ssl error: error:14090086:SSL 
routines:ssl3_get_server_certificate:certificate verify failed

The certificate on 88.198.198.21 is valid, checked with openssl s_client.

I suspect that my rspamd version is too old or needs a reconfiguration. I 
didn't follow updates for some time. My current version is 2.5-156~xenial.
I don't want to update currently. What can I do to resolve this problem? 
*Is* it resolvable with 2.5?
Does maybe my rspamd use an outdated root certificate list? I know there 
was an update involving Lets Encrypt certificate chain in December.

Thanks!

Kai