Hi folks, I've got a quick one here and apologise for the simplicity of the question but we can't for the life of us figure this out. We have a client who has two contact groups. Contact Group A and Contact Group B. Contact Group A actually contains Contact Group B. When the client sends an email to Contact Group A it comes back as undeliverable to Contact Group B, but works when sent on its own to B. Now I have worked this out as Outlook is trying to send it to the -name- of Contact Group B, believing it to be an email address, rather than to the contained actual addresses. I expanded the group within the 'To>' field and sure enough it had Contact Group B <unknown>. The issue here is, apparently this was working fine before. Have I missed something stupidly obvious? Thank you in advance for your help.