That's incorrect. 100mg can be shipped.

IATA regulations state that you can ship chemicals up to a certain deadliness aka LD50. 100mg/ml nicotine falls slightly under the limit = isn't considered DG = doesn't have any restrictions or packaging requirements :)

I believe if you follow correct hazmat packaging and pay a premium, you can exceed the 48mg/ml limit. Most mail carriers will limit nic, however, since they don't wish to implement "proper" handling for their airmail. (Others likely don't care, such as certain chinese postal services.)

Still, if one is trying to get nicotine shipped somewhere where normal shipping methods won't work, its probably a good assumption the reciever wants the shipper to play fast and loose with the law, and probably not let anyone (carriers, customs, etc) know that the substance being shipped is reasonably concentrated nicotine.