Update: Preliminary investigation revealed all suspicious letters received in Manhattan offices today to be non-toxic.  Additional testing of the substances is pending. Several of the envelopes had the following return address:

400 Sunrise Highway, Amityville, NY  11701

If you receive mail with this return address, call 911 immediately.  DO NOT OPEN the envelope or handle it further.

Several envelopes containing a white powder were sent to offices (not Jewish)  in Manhattan locations today.  Reminder: all businesses that have mailrooms should review their handling procedures with staff.  Please advise your mailroom personnel not to handle letters or packages that look suspicious (discoloration, stains, or emits an odor).  Personnel should immediately leave the area and dial 911. Personnel should make sure that no one re-enters the area until the NYPD/FDNY Hazmat Unit declares it safe.  For more information NYPD SHIELD at 718-615-7506 or www.nypdshield.org.

Find the USPS poster giving tips on how to spot suspicious mail and packages here.