Exchange External contacts and distribution lists

Hello Team,

I have a requirement to send emails to a group of people that are external to our organsation and I require the group to be displayed in the GAL.

So far I have created the people concerned as contacts in the AD and then created a distribution lsit and added the contacts to this distribution list.

The problem is when I send an email to either the individual contact or the distribution list they are not recieved.

Can anyone please advise

Many thanks

Pat