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Click your user icon, then your user name:

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Click “Preferences”:

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Click “Emails”:

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Click “Enable mailing list mode”, and select the frequency of emails:

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By default, you will be subscribed to posts in all categories. To disable notifications for a category, visit the category page:

and select the “Muted” option in the notification preference menu:

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To respond via email, simply click “Reply” in your mail client, and reply as indicated in the email footer.
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To post a new topic via email, use the following addresses:
Can it be configured to not send HTML emails?
I do not think that it is possible to change that setting on a user basis.