Publication 4482, “403(b) Tax-Sheltered Annuities for Participants,” and Publication 4483, “403(b) Tax-Sheltered Annuity Plans for Sponsors,” both list common mistakes the agency finds in these plans.
The publication for participants also highlights plan features of 403(b)s. The publication for sponsors discusses IRS products, services and assistance to help 403(b) plan sponsors keep their plans healthy.
Publication 4482 is here.
Publication 4483 is here.