Sometimes Spam mails pass through the filter, we can flag and train the filter manually.
Spam mails that gets through end up in the Incoming filter.
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Navigate to Incoming tabs from the main Dashboard.
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Click on Logs.
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Query rules by default uses timestamp, the results should show up automatically.

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Spam mails that passes through the spam filter is always on Delivered status.

Checklist the mails that are spam.

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Select Block Sender as the action, hit apply.
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Without removing the checklist, select Train as Spam as the action and hit apply again.

You're done, senders are now blocked and mails marked are trained as spam!
To Upload Messages manually,
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Navigate to the dashboard.
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On the left handside, click on Incoming > Train Messages.

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Upload your messages to train as spam or train as legitimate messages.

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Click on Continue to train uploaded messages.