Absolutely no sending in white envelopes under any circumstances. The minimum amount of protection when sending all cards is as follows:
a) Each card to be in a penny sleeve, always. b) Cards are to be placed in appropriately thick top loaders, secured by tape at the top. c) Cards to be sent in a bubble mailer.
In the event of sending a large number of cards, where individually placing each card in a top loader is not practical, the cards should be well protected between cardboard/top loaders and posted in a box or bubble mailer.
Postage methods that are NOT approved : a) Cards in a white envelope, regardless of individual card protection - sending in white envelopes is not to happen and will result in a negative being left for you. b) Cards sent in a penny sleeves or team bags without any other protection. c) Careless packing methods, such as sending cards in top loaders without tape/team bag to prevent the card slipping out and being damaged. d) Cards shipped in snap-tight cases with rounded corners. e) Any other way you can think of that will cause a card to be damaged.
Other sites do not have rules for these sorts of things, and we have seen far too many cards damaged from poor packing. The white envelopes in particular are a no no - we have it from an Aussie Post employee that these white envelopes go through an automated sorting machine, which explains some of the damage we have seen to cards/top loaders sent in plain envelopes. Bubble mailers do not go through this process, so the chances of damage are far less likely.