Fix some documentation links

[casperklein]

Description

This fixes the KMail link in our documentation.

According to this, there are three more links, that are at least temporary not available.

Should we keep or purge them?

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[polarathene]

https://tvi.al/simple-mail-server-with-docker/

Original project authors blogpost on why the project came to be IIRC, may no longer be relevant other than docker-mailserver roots. He perhaps no longer sees any reason to keep his web server going and stopped paying for it, or may not have realized (assuming bill is no longer paid intentionally/unintentionally rather than technical error).

---

https://community.rackspace.com/products/f/email-products-forum/3897/how-to-setup-postfix-with-a-mailgun-smtp-relay-when-using-multiple-domains

I haven't looked up the context of the link or contents. Rackspace is rather large so this would affect plenty of content. They may have migrated if the content is not temporarily unavailable, in which case we just have to identify the new URL, I don't think they'd have deleted it... but maybe.

---

https://www.stevejenkins.com/blog/2011/03/how-to-use-address-tagging-usertagexample-com-with-postfix/

Again I haven't looked into context or content, the article seems rather dated now (over 10 years ago). Could replace it or try import anything relevant from the resource if it's worth adding to our docs?

In this case it's not a 404, but unclear why there is an issue with their certificate since they're proxying through Cloudflare too. Perhaps a technical error or lack of maintenance..

---

We could adjust the links to archived versions too:

Wayback machine:

• https://web.archive.org/web/20201111192242/https://tvi.al/simple-mail-server-with-docker/
• https://web.archive.org/web/20201123162913/https://www.stevejenkins.com/blog/2011/03/how-to-use-address-tagging-usertagexample-com-with-postfix/

Rackspace got acquired a while back, the community forums went offline early 2019, and wayback machine doesn't have that particular page so it's likely gone for good. Might as well delete that one.

[georglauterbach]

This can no doubt go into v10.5.0 :D

[casperklein]

I've removed the three remaining dead links also. As mentioned, the blog posts were pretty old and wouldn't probably fit the current DMS status.
community.rackspace.com doesn't even have an DNS record. So I doubt, this will come back.

[github-actions]

Documentation preview for this PR is ready! 🎉

Built with commit: feb7d6f

[georglauterbach]

Just a short remaining remark: In the README, there is a dead link remaining:

docker-mailserver/README.md

Line 12 in 83231da

A production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.). Only configuration files, no SQL database. Keep it simple and versioned. Easy to [deploy](#usage) and upgrade. [Documentation][documentation::web] via MkDocs. [Why this image was created](https://tvi.al/simple-mail-server-with-docker/).

At the very end: https://tvi.al/simple-mail-server-with-docker/. As we removed this from the docs, should we remove it here as well? The link is dead after all...

[casperklein]

Just a short remaining remark: In the README, there is a dead link remaining:

This has already been addressed. See commit ef5b3a8 (#2426) and discussion above.

[georglauterbach]

Just a short remaining remark: In the README, there is a dead link remaining:

This has already been addressed. See commit ef5b3a8 (#2426) and discussion above.

I see now, had an old diff. Nice!

[wernerfred]

https://tvi.al/simple-mail-server-with-docker/ is up again, should we re-add it?
Seems like it was only a temporary issue with the hosting.

[polarathene]

should we re-add it?

I'm fine with that, it's mostly a history thing now about origins from original author where the project codebase has been modified rather heavily since.

Some parts are no longer relevant, probably obvious due to age, but might not be helpful to readers or possibly confuse them?:

I released tvial/docker-mailserver on the docker registry.
courier-imap
generate a self-signed certificate using a dedicated tool (which can be tricky...)
I'll help you and merge.

Perhaps only restore it in the docs blog post section, with context that it's the original authors announcement post? (at least that's how I view it)