If you have an immigrant visa case in process (for example, a U.S. family member has petitioned for you), and if your final interview will be held at a U.S. consulate in another country, it's likely that your application file will, at some point, be handled by an intermediary called the National Visa Center (NVC).
That's particularly true if you are on a waiting list for an available visa number. This would happen because you're not an "immediate relative" of a U.S. citizen or in another category where demand for visas is lower than supply, and your "priority date" isn't yet current. Some people wait years, during which the NVC might be the sole holder of their file.
Given the NVC's important to eventually moving your case along, it's crucial that you advise it of any changes of address or other contact information.
The NVC has no decision-making power, but plays an important administrative role. It acts as a sort of an intermediary, handling applicants' files after initial petition approval by U.S. Citizenship and Immigration Services (USCIS), maintaining these files while waiting for the applicants to have current priority dates and thus available visas, and then arranging for transfer of the file to the appropriate overseas U.S. consulate or embassy.
Depending on the type of visa you hope to qualify for, your file might be held at the NVC for anywhere from several weeks to several years or even decades.
The NVC is an independent agency, not truly a part of either USCIS or the Department of State. Therefore, you can't count on one of these agencies passing along your latest contact information.
What's more, during the months or years it takes for your case to be completed, it's not unlikely that either the U.S. petitioner (the family member or employer who filed the initial visa petition, for example on Form I-130 or I-140) or the foreign-born beneficiary (the intending immigrant) will move or get a new telephone number or email address.
For many type of immigrant applications, the beneficiary, at least, would need to submit Form AR-11 to USCIS after having moved to a new address. But this does not necessarily work for cases at the NVC. Inconvenient though this is, you might need to communicate directly with it to keep your immigration plans on track.
To do so, either call the NVC's Customer Assistance Center at 1-603-334-0700 or go to its online inquiry form. If you are worried that you might have already missed some notifications, you can also use either of these two methods to contact the NVC and ask about the status of your case.