Enable the SSL flag in /etc/dovecot.conf

Description

To allow clients to make encrypted connections the ssl flag in Dovecot's configuration file needs to be set to yes.

Edit /etc/dovecot/conf.d/10-ssl.conf and add or correct the following line:

ssl = yes

Rationale

SSL encrypt network traffic between the Dovecot server and its clients protecting user credentials, mail as it is downloaded, and clients may use SSL certificates to authenticate the server, preventing another system from impersonating the server.