The Internal Revenue Service (IRS) has provided the following guidance for U.S. citizens abroad.  This IRS guidance is posted under Federal Benefits and Obligations on www.travel.state.gov.

Can I Mail My Return and Payment?

You can mail your tax return and payment using the postal service or approved private delivery services.  A list of approved delivery services is available on IRS.gov.  If you mail a return from outside the United States, the date of filing is the postmark date.  However, if you mail a payment, separately or with your return, your payment is not considered received until the date of actual receipt.

Can I Electronically File My Return?

You can prepare and e-file your income tax return, in many cases for free.  Participating software companies make their products available through the IRS. E-File options are listed on IRS.gov.