2443dfc208
Dovecot 2.4 has a new configuration format, which is unfortunately backwards-incompatible with Dovecot 2.3. This patch adds a 2.4-compatible config, and selects which one to use based on the Dovecot version in the environment. In the future, once 2.4 becomes more common, we will drop the 2.3 config from the test. Note that we don't change the config used in the Docker image, because that is based on Debian **stable** which is still on 2.3.