The island's main Air Mauritius office is in Port Mathurin. There is also an office at the airport that opens for arrivals and departures. It's a good idea to phone the airline the day before you leave, just to make sure there's been no change to the schedule. For most of the year there are just two flights a day. Whenever you travel, book early, as seats can be hard to come by if you leave it late.
There is a luggage limit of 15kg per person (unless you have an onward connection with an airline allowing more – note that the onward connection must be leaving within 24 hours), with excess charged at Rs 150 per kilogram.