- the 10 uL of plasmid miniprep may have been splattered in the cap of the tube (AnnaF)
- the eppendorf tube may have depressurized during air shipment and allowed the 10 uL to escape and evaporate
- solution: try air-drying or blotting (Jonas) your minipreps prior to air shipment
As AnnaF wrote, the 10 uL of your plasmid could have been hidden in the cap or dispersed around the tube, making appear empty. You should check with your collaborators to be sure they centrifuged it.
According to a fedex document on shipping perishables (pdf) and a paper measuring the temp and pressure of air shipments (pdf), fedex and ups air shipments may experience low pressure environments around 0.56 - 0.74 atmospheres (atm). At these relatively low pressures, perhaps an eppendorf tube sealed at 1 atm might breach. The papers also note that ground shipments that pass over the rockies (i.e. in Colorado) may experience ~ 0.64 atm.
So perhaps your 1.5 ml eppendorf tube depressurized during the shipment?
It would be interesting to do some tests on the pressure-worthiness of eppendorf tubes.
Regarding the original question, in 2007 I prepared and shipped (fedex) a library of thousands of minipreps to hundreds of users. 1uL of miniprep was dispensed into wells of 384-well plates and airdried, then sealed with aluminum, then mailed. Users rehydrate a well with 10 uL of water. Generally it works.