OSS projects and authors are just making it too easy to enable IPv6! Not that this is a bad thing mind you, because it means there is even less reason to NOT have your services available on IPv6. We’ll take a speedy look at configuring Dovecot.
#listen = *, ::
This line lets you configure what addresses Dovecot will listen on.
* = All IPv4
:: = All IPv6
If you have specific IPs you only want Dovecot listening on, you would specify a
listen = line with comma delimited addresses for those IPs. By default Dovecot will listen on all available IPs configured on the server, as will the services you’ve decided to provide (POP3, POP3S, IMAP, IMAPS, etc.).