Relay question for Exchange gurus

[Quatermass]

We have a Distribution Group set up, which contains a mixture of recipients : normal internal addresses, and external addresses which have previously been set up as Contacts. If I email one of the Contacts direct, they get my email. However if I email the Group, the Contacts don't get it. Any ideas folks? I found this KB article Messages that are sent through Exchange 2003 to an external messaging server are blocked by Sender ID checking whose first bullet point sounds like the same issue. What do you think?

[BJG]

Is it the same whether you send email to the distribution list internally or externally...?

I'm wondering if it's this...

Q)

I have a distribution list on our Exchange server that contains internal mailboxes and external email address (contacts).
When I send email to this distribution list internally, the email gets delivered to both internal and external address.
The problem is when I send email from an outside account to the same distribution list, the email gets delivered to the internal mailboxes but NOT to the external email address (contacts)

A)

Are the external contacts set to only accept mail from authenticated users only? (it's a check box which needs to be unchecked in Exchange General tab > Delivery Restrictions button. Also make sure "Accept messages from everyone" is selected.

If the authenticated users only option is enabled, it would cause the problem you're seeing since when you send it internally, you're authenticated. However externally you're just one of the many addresses on the internet and aren't considered authenticated.

If that doesn't sort it, just send the message via OWA or configure outlook with RPC over HTTPS and do it that way.

Distribution list with external contacts : external, distribution, exchange, contacts, list

[Quatermass]

Yes, it's the same whether external or internal. We tested it from outside (GMail to Distribution Group), inside (Outlook to DG) and from outside but internal (OWA to DG). And yes, the Contacts are set to Accept Messages from Everyone.