Split and Organise documentation files (#404)

* Set global TOC collapse to false

* Split documentation

I tried to split the index.md file into logical parts, not changing the contents.
I did add a space and change one HTTP URL to HTTPS.

---------

Co-authored-by: Sean Whalen <44679+seanthegeek@users.noreply.github.com>

docs/source/dmarc.md

@@ -0,0 +1,71 @@
+# Understanding DMARC
+## Resources
+
+### DMARC guides
+
+- [Demystifying DMARC] - A complete guide to SPF, DKIM, and DMARC
+
+[demystifying dmarc]: https://seanthegeek.net/459/demystifying-dmarc/
+
+### SPF and DMARC record validation
+
+If you are looking for SPF and DMARC record validation and parsing,
+check out the sister project,
+[checkdmarc](https://domainaware.github.io/checkdmarc/).
+
+### Lookalike domains
+
+DMARC protects against domain spoofing, not lookalike domains. for open source
+lookalike domain monitoring, check out [DomainAware](https://github.com/seanthegeek/domainaware).
+
+
+## DMARC Alignment Guide
+
+DMARC ensures that SPF and DKM authentication mechanisms actually authenticate
+against the same domain that the end user sees.
+
+A message passes a DMARC check by passing DKIM or SPF, **as long as the related
+indicators are also in alignment**.
+
+```{eval-rst}
++-----------------------+-----------------------+-----------------------+
+|                       | **DKIM**              | **SPF**               |
++-----------------------+-----------------------+-----------------------+
+| **Passing**           | The signature in the  | The mail server's IP  |
+|                       | DKIM header is        | address is listed in  |
+|                       | validated using a     | the SPF record of the |
+|                       | public key that is    | domain in the SMTP    |
+|                       | published as a DNS    | envelope's mail from  |
+|                       | record of the domain  | header                |
+|                       | name specified in the |                       |
+|                       | signature             |                       |
++-----------------------+-----------------------+-----------------------+
+| **Alignment**         | The signing domain    | The domain in the     |
+|                       | aligns with the       | SMTP envelope's mail  |
+|                       | domain in the         | from header aligns    |
+|                       | message's from header | with the domain in    |
+|                       |                       | the message's from    |
+|                       |                       | header                |
++-----------------------+-----------------------+-----------------------+
+```
+
+## What if a sender won't support DKIM/DMARC?
+
+1. Some vendors don't know about DMARC yet; ask about SPF and DKIM/email
+   authentication.
+2. Check if they can send through your email relays instead of theirs.
+3. Do they really need to spoof your domain? Why not use the display
+   name instead?
+4. Worst case, have that vendor send email as a specific subdomain of
+   your domain (e.g. `noreply@news.example.com`), and then create
+   separate SPF and DMARC records on `news.example.com`, and set
+   `p=none` in that DMARC record.
+
+:::{warning}
+Do not alter the `p` or `sp` values of the DMARC record on the
+Top-Level Domain (TLD) – that would leave you vulnerable to
+spoofing of your TLD and/or any subdomain.
+:::
+
+```{include} mailing-lists.md
+```