Sorting mailing list posts

I recently spent some effort to overhaul the way I organize my email, specifically email for the many mailing lists I subscribe to. I’m pretty happy with the result, and it helped me subscribe to more mailing lists than I had before. In most of the ways that I care about, my mailing list experience is better than my experience with most web forums, now.

Sorting mailing list e-mails hierarchically

Anyone who ever used NNTP can recall the dotted, hierarchical naming scheme for news groups:


… and so on. This naming scheme means, to some degree, that groups with related content will share a common naming prefix. So, with an appropriately capable news reader, you could, for example, view content from all programming-language related news groups by matching groups against the pattern comp.lang.*.

Most mailing lists will contain a “List ID” header. For example, all mails from the Linux kernel’s “netdev” mailing list will contain the header:

List-ID: <>

If we can reverse the List ID, then mailing lists from the same organization will be naturally grouped together:


Now, the naming is not quite as content-based as news groups; rather, mailing lists run by the same organization will have the same prefix. This is good enough for my needs. I am a Fastmail customer, and they allow you to sort incoming and outgoing mail with the Sieve mail filtering language. So I added the following custom action:

if exists "list-id" {
  if header :regex "list-id" "<(([^.]+)\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+\\.)?([^.]+)>" {
    set :lower "folder" "ml.${9}${8}${7}${6}${5}${4}${3}${2}";
    fileinto :create "INBOX.${folder}";

The regular expression is a bit ugly. Sieve programs often cross organizational boundaries; here, I, the user/customer, am writing a program that will run on another organization (Fastmail)’s servers. So, unsurprisingly, the language’s capabilities are very limited, to make it harder for a malicious or buggy program to compromise the service. Notably, the language has no loops or recursion.

The regular expression above takes a string such as


and cuts it up into these groups, numbered 1 through 10:

((netdev)) (.vger) (.kernel) () () () () () (.org)

Then the expression

set :lower "folder" "ml.${9}${8}${7}${6}${5}${4}${3}${2}";

creates the variable folder with the groups substituted:


Note that I leave out the final group. This usually contains a top-level domain name, like org or net or com. I may or may not revert that decision, but I do that because there is a very small group of commonly-used TLDs and I didn’t see a point in grouping all messages that share the same TLD.

Finally, the expression

fileinto :create "INBOX.${folder}";

Files the e-mail into the constructed folder, creating the folder if it does not already exist. In Fastmail, a dot (.) is the folder separator. With this filter in place, plus an extra filter for mailing lists which use the Mailing-List header instead of List-ID, all of my mailing list e-mail is automatically sorted into a nice hierarchy:


Occasionally I view one of these folders, but more commonly, I use Fastmail’s “saved searches” feature to view many lists at once. For example, I have a few searches such as:

in:ml/* is:unread after:1d
in:ml/kernel/* is:unread after:1d
in:ml/ocaml/* is:unread after:7d
(in:kernel/* OR in:sourceforge/*) after:1d is:unread

If there is a thread that I want to follow, I ‘pin’ it, and then it will show up in my “pinned threads” view. I have not currently found a way to be notified of messages to pinned conversations.

That’s it! I was doing something similar before, filing mailing list emails into a folder based on the name of the list, but I was not reversing the domain name. Such a small change has increased the number of lists I can subscribe to without being overwhelmed.

Email versus web forums

Email is old, and it shows. However, with the right client and filters, it can be very pleasant to use. I used to follow several discourse-based forums through my web browser. However, discourse supports receiving and posting forum messages over e-mail, so after implementing my filters, I enabled this feature for the forums. Since doing so, I prefer the email experience, and almost never use the web interface.

The content is immutable

Once an e-mail is delivered to you, the sender cannot “take it back” or modify it. As long as you don’t delete your e-mails, the message is never lost. While mutability is a feature for something like a wiki, for open discussions it is important that a message cannot be modified or redacted after the fact.

You can compose cross-forum views

A web forum will never be able to compete with this feature. In the same window, I can view messages from different mailing lists, run by different organizations, who have no knowledge of each other.

Most content is plain text

Depending on who you are, this may be a pro or con for email. For me, I prefer plain text for most communication. Images and such can still be provided as attachments. Many clients will send HTML emails as well, but it is frowned upon on many of the lists I follow.

Room for improvement

What I have is not perfect. I’m happy with it, but there are a few features I’d like to have.

Search based on threads, not messages

In my saved searches, I tried to filter out code reviews by including the term:


unfortunately, this rarely works, because it is common for replies to the message to modify the subject and omit the PATCH phrase, like:

[PATCH BlueZ 1/3] storage: Add support for STATE_DIRECTORY environment variable
→ RE: [BlueZ,1/3] storage: Add support for STATE_DIRECTORY environment variable

I could try to chase these conventions and build more complicated filters, but it would be nice to include or exclude a thread if any of its messages match the filter.

Limiting the results per folder

It would be really nice to have a view that just shows the most recent N unread messages from each folder. This would give me an overview of every list without the more active lists dominating the results. This is similar to what the Fraidycat extension does for feeds, giving each feed the same amount of real estate regardless of how active it is.

Better control over notifications

The fastmail web & mobile clients allow me to be notified when messages are sent to a specific label, or from specific people, but I can’t be notified of new messages in a specific thread, or messages matching a specific search filter.

A proper desktop client

Fastmail’s mobile and web clients are quite nice, so I have been dragging my feet here. I still find myself composing messages in a text editor and then copying it into Fastmail’s web interface. I would like to setup a proper mail client on my desktop, but there are so many, and I try not to customize the software I use too much, that I am taking my time to find one with default behavior that I like. A mail client may be able to fill some of the holes I’ve described above.

Crazy idea - mailbox as a web forum

A specialized mail client could provide a web forum-like user interface for the mailing list posts in a user’s mailbox. Mailboxes could be supplemented with mailing lists archives, to show threads which existed before the user subscribed to the list. There could be one section per list id, grouped similarly to what my sieve filter accomplishes. The user could also create “dynamic” boards, which are the union of all messages in one or more folders, or all messages which match some search expression.

Is this a good idea? I’m not sure! The end result seems like it would be useful, but I think there would be a lot of details that could end up being a huge time sink. Even something as simple as deciding what messages are part of the same thread, is not as simple as you would think.