This is not the city's response when asked for its Records Retention Schedule. The official current schedule as of June 14, 2017 does not make special provision for electronic records; most categories list "Various (paper, digital)" as media type. Some categories are "permanent," but many are scheduled for only a few years' preservation or even just one.For example, electronic records are maintained for indefinite periods of time and are almost never deleted outright. In fact, as of this writing the total number of records kept by our email archiving service exceeds 7.1 million!

Of the very small number of record categories which are specifically electronic media, at least a couple have a retention period under one year. (911 calls, e.g., are scheduled for 90 days.)
According to the official schedule "correspondence," specifically including electronic mail, is retained for either 1 year, 2 years, or "until no longer of administrative value."