You can only ship from the Correos (Spanish post office) once you are in Spain. You cannot carry luggage the first day into Spain. Perhaps if you had a burro, donkey or mule you might, but not by hand.
I strongly advise against shipping from France into Spain. It can be done, but is both expensive and 'iffy.' Despite the best efforts of the EU to homogenize systems and processes across Europe, you are still dealing with individual national postal systems.
Each system treats a cross border shipment as international. This introduces extra time and costs to the process. I have had parcels go 'walkabout' from Portugal to Spain. In fact, I walked from Portugal to Santiago faster than the parcels traveled through two mail systems...
They both have very good mail tracking systems that I had on my iPhone. It was remarkable to see the 'higgly-piggily' routing and distribution system they were using.
In my direct experience, as well as many others, the best way to get luggage from SJPdP direct to Santiago is still
Express Bourricot. They pick up your luggage at your hotel or albergue the morning you walk out, or you can deposit it at their office at #31 Rue de la Citadelle, very near the SJPdP PIlgrim Office (#39). All hotel and hostel proprietors at SJPdP are familiar with their service and can assist you. Here is their website:
https://www.expressbourricot.com/
It costs about €70 to send one piece of luggage. Size and weight limits apply. But, if two people can share one piece of luggage, only for the stuff you want sent ahead, this is ideal. They run their company van twice monthly (it takes two days to drive there). Your luggage will be in a locked room at Albergue / Hostal La Salle in Santiago waiting for you. You arrive, identify yourself, a passport works great, and they unlock the door and allow you to fetch your bag.
I have done this twice and it works great. Also, if you do this, the La Salle will give you a discount on accommodations. Albergue La Salle is perhaps a 10 - 12 minute, uphill walk, from the Pilgrim Office.
Alternatively, from anywhere Spain, the easiest thing to do is to use the Correos to ship anything from an envelope to a suitcase to Ivar (see here in the forum). The option to this, is to make a lodging reservation at Santiago for your arrival, and ask that property if you can send a parcel or suitcase to them to hold for your arrival.
The Correos wil transport nearly anything. In my many visits to Ivar's workshop and office, about the only thing I have not yet seen is a bubble-wrapped spouse...
I have seen bicycles, HUGE suitcases and duffel bags, Really large corrugated boxes (needing a cart to move), and all manner of smaller suitcases and odd-shaped objects.
Thirdly, you can ship from post office to post office within Spain. The Correos has gotten into the Camino support business big-time over the past two or three years. Most reviews have been very positive so far.
IIRC, they will hold most anything sent ahead for 15 days for free. After that, there is a nominal daily charge. In my view the biggest glitch is that they might be closed when I want my stuff on arrival. That is why I favor the hotel-direct option for a short camino and Ivar for a long one.
Personally, I prefer Express Bourricot (E/B) if coming over the mountains from France and Ivar if coming from Spain on a month-long Camino. I tend to use the hotel-direct shipping option only if I am walking a short (2 week or less) camino. I do not want my stuff sitting in a hotel or albergue office longer than necessary. Both E/B and Ivar are more secure.
Hope this helps.
