Adding `internet.nl` mail tester, this testing services gives users in-depth analysis of their mail server, connectivity, DKIM/SPF/DMARC records and DNS.
The user management docs are now one page, because the division between
accounts and aliases is useless because there simply isn't enough
content to justify the split. I improved and updated the text a bit.
* docs: change some absolute links to relative links
* docs: change most hard-coded links to `edge` to point to `latest`
* Apply suggestions from code review
* docs: revert 404 page to edge and change canonical link to `latest
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Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>
