Several times we’ve heard people ask what the maximum size is for the EWS identifier. This question usually comes up when developers are designing a database schema that will store the EWS identifier in a fixed-width column. Our answer is that the EWS item identifier should be contained in a fixed-width column of 512 characters. So, how confident should you feel about defining your field at 512 characters? Well, of course we reserve the right to change the format, and the resulting maximum length of the EWS identifier. The chances of that occurring, however, are very slim. The EWS identifier format has been changed once between Exchange 2007 and 2007 SP1, early on in the adoption of EWS, but we acknowledge that changing the format at this point would have unwelcome effects on both customer and Microsoft applications that interoperate with Exchange. In short, we do not expect the EWS identifier format to change.