Corrections are the main way you teach Sortmail. Each one takes a click, and it lasts: that sender goes where you said from then on.
How to correct
Hover any row and click the move icon, or open the message and press M, then pick the category it should have been. Sortmail records the correction and writes the rule first, then files the message into the new label in your mailbox.
Move anything in Gmail and Sortmail learns. Take a message out of one Sortmail label and put it under another, in any Gmail app, and that is the same correction, with the same rule. Putting a filed message back in your inbox, with no Sortmail label, counts as a correction too. It becomes a rule only when exactly one of your categories stays in the inbox, because the inbox on its own does not say which category you meant. Archiving is not a correction. Moves made in Outlook are not read back yet, so correct Outlook mail here.
What the correction does next
It creates a rule for that exact sender address. From then on, every new message from them goes where you said, and the model is not consulted for them. A correction also outranks a rule you wrote by hand. Mail from that sender that was filed earlier stays where it is until you move it.
If you correct the same sender twice
The second correction replaces the first. There is no accumulating weight or confidence score to reason about — the most recent instruction wins, which is the only behaviour that is predictable.