Methods, apparatuses, and computer-readable media for detecting bulk electronic messages using header similarity analysis. Bulk electronic messages can be detected by parsing (115) header fields of an electronic message; associating (120) at least one constituent unit with each header field defining a set of constituent units for each header field; ascertaining (230) a feature vector for each set of constituent units; forming (240) a collection of feature vectors; and computing (250) an inner product from a set of constituent units from an additional electronic message and the collection of feature vectors from the initial electronic message resulting in a measure of similarity between the initial electronic message and the additional electronic message.