Copy and pasted from sendmybag website FAQ:
What can I send?
Whilst our name would suggest you can only send bags, we're happy to accept sturdy cardboard boxes and correctly prepared sports equipment as well as suitcases. Plastic boxes and plastic bags (including laundry bags) of any type are not acceptable.
Please bear in mind our service is designed for sending clothing, shoes, books and other items which do not require additional packaging when placed in a suitcase.
If you choose to send non-standard excess baggage items you must ensure the items are packaged thoroughly and appropriately for transportation through an automated network. Your suitcase or box may be stacked with other items and will move on automated belts and slide down sorting chutes.
Non standard excess baggage items such as electricals (TVs, PCs, Printers etc) and furniture (including flat pack) are sent at the owner's risk and are excluded from cover against damage, see our Terms of Service for more information.
While all items are handled with care, your item will move through the automated network as described above and as such we do not recommended sending items made of materials such as glass or porcelain, regardless of the level of packaging. 'Fragile' or 'this way up' stickers cannot be adhered to by the automated network.
While damage of any type is rare, complimentary cover cannot extend to damage to sports equipment or musical instruments unless they are prepared within manufacturer guidelines and sent within either a freight approved case. If using a standard soft sided or hardshell carry case this should be securely packaged within a double walled cardboard box.
Hope that helps.