If the Exchange admin marked the resource calendar to NOT accept recurring meetings, then you will have to do what you are currently doing.

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Milly Staples [MVP - Outlook]
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After furious head scratching, Emily asked:
| Currently when I schedule a reoccurring meeting in Outlook, if I
| define the resource when I do the original meeting it does not book
| it. I have to leave the room definied as an attendee send it out &
| then go back into each & every occurrence and change the room to a
| resource to book it. Is there an easier way to do this when I do the
| original meeting request?