Description

• The old Dovecot wiki link needed to be updated to the new location.
• The new docs are not entirely compatible AFAIK, thus making the existing examples/docs a bit outdated / incompatible. A warning admonition has been added early on to raise awareness to the reader.
• Minor formatting revisions to the content.

Fixes #3806

UPDATE: For additional reference on sieve, these could be considered for adding to a revision of the docs:

• https://proton.me/support/sieve-advanced-custom-filters
• https://doc.dovecot.org/configuration_manual/sieve/pigeonhole_sieve_interpreter/
• https://www.iana.org/assignments/sieve-extensions/sieve-extensions.xhtml
• https://thsmi.github.io/sieve-reference/en/
• spam: use Sieve for rewriting subject with Rspamd & SA/Amavis #3820 (comment)

Type of change

• Improvement (non-breaking change that does improve existing functionality)
• This change requires a documentation update

Checklist:

• I have added information about changes made in this PR to CHANGELOG.md

Is this a change worth highlighting in the changelog? Probably not 🤷‍♂️