It doesn't smell right.  Some question you may ask yourself...

• The IRS will not outsource mail processing to a third country, AFAIK.
• What is the notice number?  Does the content conform to the standard format?
• Does it have the taxpayer's SSN truncated?  If so, are the digits correct?
• IRS generally uses addresses with dedicated ZIP codes and not street addresses for PDS.  And addresses for PDS don't come with Mail Stop numbers.

There is probably a phone number they suggest the taxpayer to call for questions.  It is most likely not an IRS number if you check (although it may look like one with a digit changed or numbers transposed).  They are probably hoping the taxpayer, knowing he/she is overseas, would call rather than correspond by mail so that they could extract information from him/her during the call.

I'd call the PPS to check that out, provided you are a third party designee or have a PoA.  Even if it's real, I wouldn't submit anything without first verifying the authenticity of the notice with the IRS.

If the notice turns out to be a scam but they have your client's mailing address, know that they filed an international return, and the SSN (whether or not truncated) is correct, your client should check his/her credit report, etc., and take the necessary actions as his/her personal data may have been breached.