Looking at my inbox I would suspect the major culprit to be marketing mail. By far the longest subject lines come from marketing messages, most of which are usi

Looking at my inbox I would suspect the major culprit to be marketing mail. By far the longest subject lines come from marketing messages, most of which are using the subject line to make their plea or call to action. Emails from real people appear to have short subject lines. From my own experience, too, I tend to avoid wordy subject lines, saving detail for the message body. The listserve option seems about the least likely to me simply because listserves have existed for a very long time. Unless mailing list names became much longer I would suspect that any changes in subject length would simply be in following larger trends (for example, the larger screens option).