Feature request: exclude IP/network in allow_nets extra field

[Zhang Huangbin]

> On Apr 30, 2019, at 2:35 PM, Sami Ketola via dovecot <dovecot at dovecot.org> wrote:
> 
> Just create another passdb for these premium users before the actual passdb and add skip = authenticated to the actual passdb.

Dear Sami,

Thank you for the suggestion.

Adding more passdb is not ideal at all, if we have more access policies, we don't want to add more and more userdb/passdb.
Dovecot already supports syntax "allow_nets=a.b.c.d", we just need something like "!" mark to exclude some IP/networks.