Hi!

Since Ubuntu 20.04 LTS is nowadays available, we have dropped 16.04 support from 2.3.13 as per policy of supporting two latest releases of operating system.

Dovecot 2.3.11.3 is latest version we provide packages for 16.04.

Please find Ubuntu 20.04 packages at https://repo.dovecot.org/

Kind regards, Aki Tuomi Open-Xchange oy