The IRS uses these determinations of the difference between an employee and a subcontractor:
Behavioral: does the company control or have the right to control what the worker does and how the worker does his or her job?
Financial:Are the business aspects of the worker's job controlled by the payer? (these include things like how worker is paid, whether expenses are reimbursed, who provides tools/supplies, etc.
Type of Relationship:Are there written contracts or employee type benefits (i.e. pension plan, insurance, vacation pay, etc.)? Will the relationship continue and is the work performed a key aspect of the business?*
*http://www.irs.gov/businesses/small/...=99921,00.html
Now that you are properly confused,

here is a more understandable source of information:
"The IRS has developed a list of 20 factors it uses to test employee or subcontractor status. The Department of Labor and state boards will normally follow these as well. Here are the twenty factors you should be aware of before deciding to call an employee an independent contractor.
1. Does the business require the worker to follow their instructions on how work is to be performed? If yes, this indicates employee status. An independent contractor will generally decide how the project should be completed and use his own methodology.
2. Does the business provide training to the worker? If you're hiring a person for a job they are not trained for and providing them with the training to carry it out, that person is probably an employee. There can be exceptions based on the facts and circumstances, but if you fail this test, you might lose no matter how many of the others you pass.
3. Are the worker’s services a substantial or integral part of the business? This indicates employee status because it indicates the business maintains direction and control over the worker.
4. Does the business require the worker to perform all services personally? Independent contractors may have their own employees or at least should have the option of hiring other contractors to perform their work. Agreements for personal services indicate employee status.
5. Does the business hire, supervise and pay the worker’s assistants? If so, this is a strong indication of employee status. Let the independent contractor pay his or her own assistants.
6. Does the business have an ongoing relationship with the worker? This one is a stretch since many businesses maintain lifelong relationships with contractors whose work they like. But the IRS views this as an indication of employee status.
7. Does the business set the worker’s schedule and hours? Independent contractors generally set their own work schedules. If the contractor must work certain hours because of required interrelationships with your employees or to take advantage of down time for computer-related work, document these facts.
8. Does the business require the worker full-time? This is an indication of employee status because the business controls their availability and prevents them from working on other clients.
9. Does the business provide the workspace? Contractors who work off-site are more likely to be classified an independent contractor.
10. Does the business determine the order or sequence in which work is completed? Indicates employee status. If specific schedules are required, document them in the contract with the reasoning for doing so.
11. Does the business require oral or written reports? The IRS believes regular written or oral reports detailing the work completed indicates employee status. In reality, this is, and should be, expected from independent contractors as well.
12. Does the business pay by the hour, week or month? This indicates employee status. See our comments at the end of this article on this issue.
13. Does the business pay expenses? This is an indication that the business is directing the Independent contractor's business activities. Make sure the independent contractor pays the expenses and bills you for reimbursement.
14. Does the business provide tools and equipment for the worker? Independent contractors would normally provide their own tools and equipment.
15. Does the worker have a significant investment in their own facilities? If the contractor maintains his own office space, computer equipment, tools, etc., this is a good indication that they are an independent contractor.
16. Does the worker have profits and losses independent of the business? This is an indication that the contractor is running his own bona fide business and is an independent contractor.
17. Does the worker have multiple clients? Working with multiple clients generally indicates independent contractor status.
18. Does the worker market their services to the general public? Employees do not generally market their services to the general public.
19. Does the business have the right to discharge the worker at any time? This suggests employee status. An independent contractor would only be discharged for failure to meet contract specifications.
20. Does the worker have the right to quit at any time? An independent contractor is under contract and cannot quit until the project is completed."**
**http://www.peaksbc.com/Articles/empl...t_contract.htm
I always say it's not what you know, it's knowing where to look.
Short version? I think you are probably safe from being considered an employee, even if you DO use your client's company's email system for HIS work. I 'spect you have your own business email for all other contacts...