Hello,
Not sure if this is the right place to post this, but the ssl certificate of the repo.dovecot.org server expired on the 9th of January.
It's giving an error via the browser and via the apt command in Debian:
W: Failed to fetch https://repo.dovecot.org/ce-2.3-latest/debian/jessie/dists/jessie/main/binary-amd64/Packages server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
Cheers!
Filipe Carvalho