[sieve] Restrict redirects to own domain only

[Ralph Seichter]

On 16.10.2018 15:43, Yassine Chaouche wrote:

> I don't fully understand how could this prevent them from forwarding
> to any other domain by other means, for example by using a managesieve-
> able client

Well, your OP made no mention of your environment. ;-) You posted on the
Dovecot mailing list, so I suppose we know what your IMAP server is, but
you mentioned nothing beyond that.

I made the assumption that your users are allowed to use sieve, based on
the subject line, but you did not elaborate on how they use it. Simplest
form: Sieve files. If you generate the files, you can screen the content
and also keep them read-only for users.

If you have important restrictions/conditions, you need to mention them
to us.

-Ralph