Use of Multi Lookup fields

Use of Multi Lookup fields

Hi, 

I wondered if anyone could help. I am trying to develop an automation that would send an email to a list of preferred suppliers associated to an account when a booking is created. I assumed this would be done using the multi lookup field, but I can't quite work it out.

At the moment I have a multi lookup field created between accounts and contacts, but I can't work out how to pull the contact list through to bookings when a new one is created. Is it a case of needing to create a custom function, am what I trying to achieve not possible or is there a simpler solution.

Would anyone be able to help?