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The Mailroom / The channel grid
Eight kinds by five channels
The channel grid: which kind of message may travel where
A channel is not a preference, it is a constraint. Some kinds of message cannot legally or practically travel on some channels, one channel per kind is treated as mandatory, and the eight by five grid has a specific answer in each of its forty cells.
Desk spec
- grid cells
- 40
- permitted
- 24
- refused
- 16
- mandatory
- 1 per kind
the five kindsA receipt records something that already happened, marketing promotes something, a service note explains a state of the account, a security alert says something changed, and a legal notice is the message whose arrival is itself a step.
the two switchesOne stops marketing and nothing else - 12 of 50 messages on the samples. The other does not stop anything: it changes the channel the remaining 38 travel on, which changes how they arrive and what they prove.
the three countsSent is what the operator's log holds (50 of 50), arrived is what a delivery receipt shows (48 of 50), and read is what a read receipt shows (21 of 50). Three counts, routinely called one.
Direct answerEight kinds of message are sent across five channels - email, the in-app inbox, push, SMS and post - and twenty-four of the forty possible combinations are permitted, sixteen are refused, and each kind has one channel treated as mandatory. The refusals are usually about length, permanence or evidence, not about cost.
The grid, cell by cell
The grid below is the whole desk's map. Read down a kind and the row shows where it may go; read across a channel and the column shows what may be carried on it.
sample C - counting the grid
kinds = 8, channels = 5 -> 8 x 5 = 40 cells
permitted combinations = 24 -> 24 / 40 = 60.0%
refused combinations = 16 -> 16 / 40 = 40.0%
mandatory channels = 8, one per kind
permitted per channel = email 8, in-app 6, push 4, SMS 3, post 3 = 24
refused per channel = in-app 2, push 4, SMS 5, post 5 = 16
so the widest channel carries all eight kinds, and the two narrowest carry three.
Sample C - what the grid refuses, and why
| Refusal | Cells | Reason it is refused |
|---|
| a long document on a channel that truncates | 5 | a statement or a notice cut to 160 characters is not the document |
| a message the channel cannot evidence later | 7 | no durable copy, so the arrival proves nothing |
| a message the reader only sees when signed in | 2 | an alert or a notice the account cannot be reached with |
| a message with no legal reason on an expensive channel | 2 | a service note by post costs 1,550 times the same note by email |
| four refusals | 16 | only two of the sixteen are refused for cost rather than for the text |
The mandatory channel is the one that survives
Each kind names one channel that must be used, and for the four unswitchable kinds it is usually the channel that leaves a durable copy. That is what makes the second switch in the previous page a routing decision rather than a filter.
sample C and D - the mandatory channel, and the time it takes
receipt mandatory channel: email arrival 0.9 s
marketing mandatory channel: email arrival 0.9 s
service note mandatory channel: email arrival 0.9 s
security alert mandatory channel: email + SMS arrival 0.9 s / 3.4 s
legal notice mandatory channel: post or email arrival 2 d 6 h / 0.9 s
the two channels a notice may use differ by 216,000 times in arrival time,
so the choice of the pair is already a choice about the notice window.
The grid on the home page is drawn from this same set of forty cells, so the two cannot disagree: eight rows, five columns, twenty-four permitted cells and sixteen refused ones.
What the grid is for
A reader who knows the grid can tell three things without asking anyone: whether a message could plausibly have come the way it did, which channel to keep open for notices, and when a channel choice has quietly shortened a window.
- Check the channel against the kind: a legal notice that only ever arrives by push is not normal.
- Keep the mandatory channel open for alerts and notices, even if it is the noisiest one.
- Treat a channel move as a change to arrival time, not just to noise.
- Note which channels leave a copy you can retrieve later - email and post do, push and SMS usually do not.
- Count what arrives where before changing a preference, so the change has a baseline to compare with.
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