certificate verify failed

[HoffmannP]

On startup imapfilter issues an error saying

imapfilter: initiating SSL connection to imap.$domain.$tld; error:14090086:SSL
    routines:ssl3_get_server_certificate:certificate verify failed

I tried to debug the issue using

openssl s_client -connect imap.$domain.$tld:993 -status

but this looked unsuspicious.

Any idea how I could proceed?

[lefcha]

What happens if you specify at the top of your config file options.hostname = false?