Include publication data as metadata in hyperkitty generated archives
By adding metadata in the pages generated by Hyperkitty, Search engines can detect the date of the publication of the content. When showing results from hyperkitty archives, the Search engines can then show when the text was published. Here is an example of a webpage with this information:
<!doctype html><html>
<head>
<script type='application/ld+json'>{"@context":"https://schema.org","@type":"NewsArticle",
"datePublished": "2023-02-02T050607Z"}</script>
</head>
<body>
See the head-section. It contains datePublished rich metadata.
</body>
</html>
It can be validated at https://search.google.com/test/rich-results .
For other projects I use the type-Event and Google then shows (sometimes) in search results the date, when the event was published.
See also https://developers.google.com/search/docs/appearance/structured-data/article for a more complete example on rich elements. Hyperkitty might include also name of the author.
Adding this information makes sense for public archives.