Howto disable external Email send to a group.

[Handyman]

In Exchange, one could remove the SMTP address from a DL and add a x400 address so its still a valid email address but people outside the company cannot Email to it. Later Exchange had some option to realize the same effect.

I’d like to know how can i configure Email groups so that they cannot receive Email from outside, but only be used by internal users.
Only a few Email groups need to be Email-able from the outside.

(to reduce spam, and phishing of Email addresses)

I would like to know if there is some configurable setting to do this inside kopano,

As an alternatie I’m thinking of adding a @local Email domain, which is not registered in DNS externally and so can only be reached internally, but thats quite a hassle to configure (sender ID etc). And not sure if that will be fine for all clients (Outlouk and webmail mobile).