Hello heascook:
If you can receive mail there, then yes, please use your mother's address in Maryland for your 2016 tax returns. That would seem to make the most sense. Of course, if you have an alternative Maryland address (like another family member or a trusted friend) then you could use that as well.
Essentially, according to Maryland state law, you will retain your Maryland "domicile" (which is a well-established legal concept) for state tax purposes, unless one of two things happen. One, you establish a tax "domicile" in another US state; or two, you become the citizen of a foreign country and give up your US citizenship. It doesn't matter if you continue to physically live in Germany, or elsewhere, for years and years -- you cannot rid yourself of your Maryland state tax domicile, except in one of the two ways just described.
Yes, it's a pretty tough standard and a burden to meet. If you were able to utilize the Foreign Earned Income Exclusion (see the rules for IRS Form 2555 at the following link: <a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-pdf/i2555.pdf">https://www.irs.gov/pub/irs-pdf/i2555.pdf</a> ) then your Maryland taxes wouldn't matter as much, because you could exclude much or most of your overseas income for state tax purposes too.
However, since you work for the United States government (whether in a civilian capacity or a military capacity it doesn't matter), you aren't eligible for the foreign earned income exclusion. So, that's not an option. Civilians not working for the US government, or those who are self-employed, can take advantage of the Foreign Earned Income Exclusion as long as they meet certain tests.
Realistically, you could return to the United States at some point, on let's say a very long vacation for example, and attempt to establish residency in a state with no income taxes, like Florida for example (get a Florida drivers license, register to vote there, have all of your bank accounts and credit cards transferred there, etc.). That could allow you to change your state tax domicile, and would be a way to avoid Maryland taxes in future years, as well as the obligation to file future tax returns there -- but this is a big step to take.
Unfortunately, the Maryland state tax system is fairly difficult to avoid, and doesn't favor expats.
Thank you for asking these follow-up questions, and good luck to you.
