dovecot - Jan 2015 - Dovecot & gethostbyname() vulnerability

So just a quick note:

Dovecot in general doesn't do DNS lookups, except the ones in configuration
files and such. So I don't think there are any Dovecot setups which do DNS
lookups for untrusted hostnames.

Also, gethostbyname() is used only if IPv6 support isn't compiled into
Dovecot. And IPv6 support is enabled by default if the libc is detected to
support it, so pretty much all systems use it.