Deleters v. Keepers: Deleters are users who habitually delete e-mails from their inbox. One user reported deleting up to 50% of her incoming e-mail after having answered it. Others keep an even smaller percentage of e-mails: Some ETH students delete almost all of their e-mail after having processed it, a decision which I attribute to privacy concerns and the illusion of strictly limited storage space on student e-mail accounts: As freshmen, they learned that there was a 50 MB storage limit on e-mail. Space is now unlimited, but habits are hard to unlearn. Another motivation for this behavior is "keeping the inbox clean", which some feel is better done by deleting than by archiving or sorting e-mail into folders.
Sorters v. Inboxers: Some users keep almost all their e-mail in their inbox, and have no sophisticated hierarchies to file e-mail into. Others typically file away incoming e-mails – either into a multi-layer folder hierarchy. GMail users like to use archiving as a way to store e-mail without seeing it in their inbox.
Writing filters vs. manual sorting: Many reported being too lazy or dumb to write filters and prefer to sort their e-mail manually, especially when they receive just a few e-mails per day. Very few fine-tune their filters to catch more than just a couple of newsletters.
Folders vs. Search Folders vs. Labels: Most Sorters have a number of folders to put their e-mail into. This can range from a simple work / private categorization to a complex hierarchy of folders for each subproject the user is working on.
GMail introduced the concept of "Labels": While each e-mail ends up in the inbox, multiple tags can be attached to each message. Each label can be used as a view over the users inbox and archive – it is materialized when the user clicks on the label. Users don't seem to apply labels manually, but let filters do the work.
Thunderbird and other mail clients have "Search Folders", which look like normal folders in the user hierarchy, but are actually views on the user's total e-mail showing all messages matching a search query. No one seems to be using these.
Ways of Marking as TODO: Many have found a way to assign priorities to e-mails. One user sorted incoming e-mails into folders for 'now', 'daily', and 'weekly', and processed e-mails according to these intervals. That was, of course, before giving up on this scheme because it was too complicated.
A commenter on the previous post uses the keys 1-5 to assign Mozilla Thunderbird's labels to incoming e-mail.
I used to flag important e-mails in Thunderbird but gave up on it because I'd forget about them when they dropped "below the fold" of the first page. Instead, I now use the same as so many others: keeping messages unread to mark them as still needing attention.
Even this strategy doesn't help e-mails from going unprocessed. One user wrote: "I tend to think that I leave emails that I still need to answer/work on marked as unread. But my 'unread' pile has aggregated to 870 emails at the moment."
Search vs. QuickSearch: GMail users like their full-text search and use it often. Users of Outlook, Thunderbird, and Lotus Notes dread full-text search, because it takes so long to get results. However, the QuickSearch box seems to be quite popular with Thunderbird users.
The problem with all search approaches, however, is coming up with just the right keywords to find the e-mail you want.
There seems to be lots of room for improvement in organizing and viewing e-mail, as well as educating users. I'll be trying out some ideas in the next weeks and will keep you posted.
Thanks to all interviewees for their input plus Fabian Siegel and Bálint Miklós for reviewing drafts of this.