What rules have to be followed for retaining board member emails regarding school district business?

All records regarding the public’s business are public records.  This means that any correspondence by board members regarding the district are subject to the public records law.

The rules that govern retention of correspondence records are contained in OAR 166-400-0010

Correspondence by board members (and anyone else in the district)  that must be retained includes written or electronic letters, memos, and  notes that communicate formal approvals, direction for action, and information about contracts, purchases, grants, personnel and particular projects or programs.  The actual length of time the correspondence must be kept depends on the subject of the correspondence. 

To check the specific length of time you must look at the OAR 166-400-0010 - 0040

For more information on this question, Ask OSBA.