Complex sentence: The other approximately 90 overseas U.S. Embassy post offices fall under the management oversight of the Services and so are known as either as APOs or FPOs, however, many will be switching to the DPO address.
Split into simpler sentences: The other approximately 90 overseas U.S. Embassy post offices fall under the management oversight of the Services and so are known as either APOs or FPOs. However, many will be switching to the DPO address.