Russell Coker: Solving Spam and Phishing for Corporations
Centralisation and Corporations
An advantage of a medium to large company is that it permits specialisation. For example I m currently working in the IT department of a medium sized company and because we have standardised hardware (Dell Latitude and Precision laptops, Dell Precision Tower workstations, and Dell PowerEdge servers) and I am involved in fixing all Linux compatibility issues on that I can fix most problems in a small fraction of the time that I would take to fix on a random computer. There is scope for a lot of debate about the extent to which companies should standardise and centralise things. But for computer problems which can escalate quickly from minor to serious if not approached in the correct manner it s clear that a good deal of centralisation is appropriate.
For people doing technical computer work such as programming there s a large portion of the employees who are computer hobbyists who like to fiddle with computers. But if the support system is run well even they will appreciate having computers just work most of the time and for a large portion of the failures having someone immediately recognise the problem, like the issues with NVidia drivers that I have documented so that first line support can implement workarounds without the need for a lengthy investigation.
A big problem with email in the modern Internet is the prevalence of Phishing scams. The current corporate approach to this is to send out test Phishing email to people and then force computer security training on everyone who clicks on them. One problem with this is that attackers only need to fool one person on one occasion and when you have hundreds of people doing something on rare occasions that s not part of their core work they will periodically get it wrong. When every test Phishing run finds several people who need extra training it seems obvious to me that this isn t a solution that s working well. I will concede that the majority of people who click on the test Phishing email would probably realise their mistake if asked to enter the password for the corporate email system, but I think it s still clear that this isn t a great solution.
Let s imagine for the sake of discussion that everyone in a company was 100% accurate at identifying Phishing email and other scam email, if that was the case would the problem be solved? I believe that even in that hypothetical case it would not be a solved problem due to the wasted time and concentration. People can spend minutes determining if a single email is legitimate. On many occasions I have had relatives and clients forward me email because they are unsure if it s valid, it s great that they seek expert advice when they are unsure about things but it would be better if they didn t have to go to that effort. What we ideally want to do is centralise the anti-Phishing and anti-spam work to a small group of people who are actually good at it and who can recognise patterns by seeing larger quantities of spam. When a spam or Phishing message is sent to 600 people in a company you don t want 600 people to individually consider it, you want one person to recognise it and delete/block all 600. If 600 people each spend one minute considering the matter then that s 10 work hours wasted!
The Rationale for Human Filtering
For personal email human filtering usually isn t viable because people want privacy. But corporate email isn t private, it s expected that the company can read it under certain circumstances (in most jurisdictions) and having email open in public areas of the office where colleagues might see it is expected. You can visit gmail.com on your lunch break to read personal email but every company policy (and common sense) says to not have actually private correspondence on company systems.
The amount of time spent by reception staff in sorting out such email would be less than that taken by individuals. When someone sends a spam to everyone in the company instead of 500 people each spending a couple of minutes working out whether it s legit you have one person who s good at recognising spam (because it s their job) who clicks on a remove mail from this sender from all mailboxes button and 500 messages are deleted and the sender is blocked.
Delaying email would be a concern. It s standard practice for CEOs (and C*Os at larger companies) to have a PA receive their email and forward the ones that need their attention. So human vetting of email can work without unreasonable delays. If we had someone checking all email for the entire company probably email to the senior people would never get noticeably delayed and while people like me would get their mail delayed on occasion people doing technical work generally don t have notifications turned on for email because it s a distraction and a fast response isn t needed. There are a few senders where fast response is required, which is mostly corporations sending a click this link within 10 minutes to confirm your password change email. Setting up rules for all such senders that are relevant to work wouldn t be difficult to do.
How to Solve This
Spam and Phishing became serious problems over 20 years ago and we have had 20 years of evolution of email filtering which still hasn t solved the problem. The vast majority of email addresses in use are run by major managed service providers and they haven t managed to filter out spam/phishing mail effectively so I think we should assume that it s not going to be solved by filtering. There is talk about what AI technology might do for filtering spam/phishing but that same technology can product better crafted hostile email to avoid filters.
An additional complication for corporate email filtering is that some criteria that are used to filter personal email don t apply to corporate mail. If someone sends email to me personally about millions of dollars then it s obviously not legit. If someone sends email to a company then it could be legit. Companies routinely have people emailing potential clients about how their products can save millions of dollars and make purchases over a million dollars. This is not a problem that s impossible to solve, it s just an extra difficulty that reduces the efficiency of filters.
It seems to me that the best solution to the problem involves having all mail filtered by a human. A company could configure their mail server to not accept direct external mail for any employee s address. Then people could email files to colleagues etc without any restriction but spam and phishing wouldn t be a problem. The issue is how to manage inbound mail. One possibility is to have addresses of the form it+russell.coker@example.com (for me as an employee in the IT department) and you would have a team of people who would read those mailboxes and forward mail to the right people if it seemed legit. Having addresses like it+russell.coker means that all mail to the IT department would be received into folders of the same account and they could be filtered by someone with suitable security level and not require any special configuration of the mail server. So the person who read the is mailbox would have a folder named russell.coker receiving mail addressed to me. The system could be configured to automate the processing of mail from known good addresses (and even domains), so they could just put in a rule saying that when Dell sends DMARC authenticated mail to is+$USER it gets immediately directed to $USER. This is the sort of thing that can be automated in the email client (mail filtering is becoming a common feature in MUAs).
For a FOSS implementation of such things the server side of it (including extracting account data from a directory to determine which department a user is in) would be about a day s work and then an option would be to modify a webmail program to have extra functionality for approving senders and sending change requests to the server to automatically direct future mail from the same sender. As an aside I have previously worked on a project that had a modified version of the Horde webmail system to do this sort of thing for challenge-response email and adding certain automated messages to the allow-list.
The Change
One of the first things to do is configuring the system to add every recipient of an outbound message to the allow list for receiving a reply. Having a script go through the sent-mail folders of all accounts and adding the recipients to the allow lists would be easy and catch the common cases.
But even with processing the sent mail folders going from a working system without such things to a system like this will take some time for the initial work of adding addresses to the allow lists, particularly for domain wide additions of all the sites that send password confirmation messages. You would need rules to direct inbound mail to the old addresses to the new style and then address a huge amount of mail that needs to be categorised. If you have 600 employees and the average amount of time taken on the first day is 10 minutes per user then that s 100 hours of work, 12 work days. If you had everyone from the IT department, reception, and executive assistants working on it that would be viable. After about a week there wouldn t be much work involved in maintaining it. Then after that it would be a net win for the company.
The Benefits
If the average employee spends one minute a day dealing with spam and phishing email then with 600 employees that s 10 hours of wasted time per day. Effectively wasting one employee s work! I m sure that s the low end of the range, 5 minutes average per day doesn t seem unreasonable especially when people are unsure about phishing email and send it to Slack so multiple employees spend time analysing it. So you could have 5 employees being wasted by hostile email and avoiding that would take a fraction of the time of a few people adding up to less than an hour of total work per day.
Then there s the training time for phishing mail. Instead of having every employee spend half an hour doing email security training every few months (that s 300 hours or 7.5 working weeks every time you do it) you just train the few experts.
In addition to saving time there are significant security benefits to having experts deal with possibly hostile email. Someone who deals with a lot of phishing email is much less likely to be tricked.
Will They Do It?
They probably won t do it any time soon. I don t think it s expensive enough for companies yet. Maybe government agencies already have equivalent measures in place, but for regular corporations it s probably regarded as too difficult to change anything and the costs aren t obvious. I have been unsuccessful in suggesting that managers spend slightly more on computer hardware to save significant amounts of worker time for 30 years.
It would be fantastic if all those AI companies dedicated some time to make
their web crawlers smarter (what about using AI?). Noawadays most of them still
stupidly follow every link on a Git frontend.
Hint: Changing the display options does not provide more training data!
Notes to self. And anyone else who might find them useful. Following are some ssacli commands which I use infrequently enough that they fall out of cache. This may repeat information in other blogs, but since I search my posts first when commands slip my mind, I thought I d include them here, too.
Our Debian User Group met on November 2nd after a somewhat longer summer hiatus
than normal. It was lovely to see a bunch of people again and to be able to
dedicate a whole day to hacking :)
Here is what we did:
lavamind:
In basically every engineering organization I ve ever regarded as particularly
high functioning, I ve sat through one specific recurring conversation which is
not a conversation about complexity . Things are good or bad because they
are or aren t complex, architectures needs to be redone because it s too
complex some refactor of whatever it is won t work because it s too complex.
You may have even been a part of some of these conversations or even been
the one advocating for simple light-weight solutions. I ve done it. Many times.
Rarely, if ever, do we talk about complexity within its rightful context
complexity for whom. Is a solution complex because it s complex for the
end user? Is it complex if it s complex for an API consumer? Is it complex if
it s complex for the person maintaining the API service? Is it complex if it s
complex for someone outside the team maintaining it to understand?
Complexity within a problem domain I ve come to believe, is fairly zero-sum
there s a fixed amount of complexity in the problem to be solved, and you can
choose to either solve it, or leave it for those downstream of you
to solve that problem on their own.
That being said, while I believe there is a lower bound in complexity to
contend with for a problem, I do not believe there is an upper bound to the
complexity of solutions possible. It is always possible, and in fact, very
likely that teams create problems for themselves while trying to solve a
problem. The rest of this post is talking to the lower bound. When getting
feedback on an early draft of this blog post, I ve been informed that Fred
Brooks coined a term for what I call lower bound complexity Essential
Complexity , in the paper
Like each month, have a look at the work funded by 
I was interested in learning about 
The topic of this posting already tells you that an old Unix guy tells
stories about old techniques.
I'm a happy NIS (formerly YP) user since 30+ years. I started using it
with SunOS 4.0, later using it with Solaris and with Linux since 1999.
In the past, a colleague wasn't happyly using NIS+ when he couldn't
log in as root after a short time because of some well known bugs and wrong
configs. NIS+ was also much slower than my NIS setup. I know
organisations using NIS for more than 80.000 user accounts in 2024.
I know the security implications of NIS but I can live with them,
because I manage all computers in the network that have access to the
NIS maps. And NIS on Linux offers to use shadow maps, which are only
accessible to the root account. My users are forced to use very
long passwords.
Unfortunately NIS support for the PAM modules was removed in Debian
in pam 1.4.0-13, which means Debian 12 (bookworm) is
lacking NIS support in PAM, but otherwise it is still supported.
This only affects changing the NIS password via passwd. You can still
authenticate users and use other NIS maps.
But 
Dear Debian community,
this is Bits from DPL for October. In addition to a summary of my
recent activities, I aim to include newsworthy developments within
Debian that might be of interest to the broader community. I believe
this provides valuable insights and foster a sense of connection across
our diverse projects. Also, I welcome your feedback on the format and
focus of these Bits, as community input helps shape their value.
Ada Lovelace Day 2024
As outlined in my platform, I'm committed to increasing the diversity of
Debian developers. I hope the recent article celebrating Ada Lovelace
Day 2024 featuring interviews with 
The coffee shop Ibtehal and me used to visit during the midnight
Grating at a chemist shop in Mombasa, Kenya
Me with players at the Nairobi Gymkhana Club
Cricket pitch at the Nairobi Gymkhana Club
A view of the cricket ground inside the Nairobi Gymkhana Club
Scoreboard at the Nairobi Gymkhana cricket ground
A matatu with a Notorious BIG portrait.
Inside the Giraffe Center
SGR train at Nairobi Terminus.
Interior of the SGR train
Mombasa Terminus station.
The balcony at Tulia Backpackers Hostel had a nice view of the ocean.
A room inside the hostel with fans and mosquito nets on the beds
Nyali beach is a white sand beach
This is the ferry service for crossing the river.
Diani beach is a popular beach in Kenya. It is a white sand beach.
Selfie with truck drivers who gave me the free ride
Newspapers at a stand in Kenya covering news on the airport closure
Spanish Omelette served in breakfast at Nairobi Transit Hotel
Ugali with eggs.