The plan was to run a Postfix secondary MX inside a docker container.
Below are many links that might help me to get that going.
For now, I think this is the shortlist of solutions to try:
- Docker Mailserver
- Mailcow
- Mailu
Archive for the ‘Communications Development’ Category
Some notes on running Postfix inside a docker container
Posted by jpluimers on 2025/11/14
Posted in *nix, *nix-tools, Cloud, Communications Development, Containers, Development, Docker, Infrastructure, Internet protocol suite, Kubernetes (k8n), postfix, Power User, SMTP | Tagged: 254, 29, 52, 787, DMARC, domains, set | Leave a Comment »
roehling/postsrsd: Postfix Sender Rewriting Scheme daemon
Posted by jpluimers on 2025/11/12
This finally made me perform the (long overdue) migration from Sendmail to Postfix:
The Sender Rewriting Scheme (SRS) is a technique to forward mails from domains which deploy the Sender Policy Framework (SPF) to prohibit other Mail Transfer Agents (MTAs) from sending mails on their behalf. With SRS, an MTA can circumvent SPF restrictions by replacing the envelope sender with a temporary email address from one of their own domains. This temporary address is bound to the original sender and only valid for a certain amount of time, which prevents abuse by spammers.
[Wayback/Archive] roehling/postsrsd: Postfix Sender Rewriting Scheme daemon
Via a long queste to figure out why Gmail every now and then bounces forwarded messages because of Sender Policy Framework (SPF). Below are a few of the links that brought me here in mostly reverse order, but first some links that should help me further on the topic of Postfix virtual aliases.
The sendmail setup had some features not covered below (like a catch-all forward for email to addresses virtual domains not covered by a virtual alias) which I hopefully can cover later.
One thing learned both over the past decades and related postfix material: use separate servers or containers for each of your functions. So do not mix web-hosting, outgoing mail, incoming mail, fail2ban and others on the same server.
Links:
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Posted in *nix, *nix-tools, Communications Development, Development, Internet protocol suite, postfix, Power User, sendmail, SMTP | Tagged: Reload | Leave a Comment »
Some ADS-B API link notes (hoping to be able to get from/to airport data from it)
Posted by jpluimers on 2025/10/28
For my link archive initiated because I was trying to find out why ADS-B Exchange does not list originating and destination airports for flights, then on how to get at that data.
It is grouped in a few parts, starting with:
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Posted in Communications Development, Development, HTTP, Internet protocol suite, JavaScript/ECMAScript, JSON, REST, Scripting, Software Development, TCP, Web Development | Leave a Comment »
GitHub – rbwebdev/lemmings-page-404: My 404 page with a little game of Lemmings
Posted by jpluimers on 2025/08/26
Last week I wrote about Example how not to return a HTPP-500 result: Amazon DE – Tut uns Leid!.
Today I found https://archive.is/undefined which consistently returns a HTTP 404 in the HTTP result.
It reminded me of an old (well, what is old anyway <g>) post Best 404 page ever. back in the days (returning both 404 in the HTTP result and page content) I did not yet archive outgoing links (it took me a few more years to realise many URLs are ephemeral and have queued up a post on that for early next year), and found out the site has changed since then. Time for archived and updated links, and a repository too as by now the source has been published on GitHub:
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Posted in Communications Development, Development, HTML, HTTP, Internet protocol suite, Software Development, Web Development | Leave a Comment »
Example how not to return a HTPP-500 result: Amazon DE – Tut uns Leid!
Posted by jpluimers on 2025/08/14
Amazon shows how not to return an HTTP 500 (Internal Server Error) result page: a page with content 500, but result HTTP 200 (OK).
[Wayback] https://www.amazon.de/errors/500
--jeroen
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Posted in Communications Development, Development, HTML, HTTP, Internet protocol suite, Software Development, TCP, Web Development | Leave a Comment »
In case I need a small 5-port managed switch that can do port-mirroring: GS305E | Easy Smart Managed Essentials Switch | NETGEAR Support
Posted by jpluimers on 2025/08/13
[Wayback/Archive] GS305E | Easy Smart Managed Essentials Switch | NETGEAR Support which can do many-to-one port mirroring.
This is a newer and cheaper hardware revision than the:
- GS105Ev2 (which is managed and can do port-mirroring, and is confusingly sold as GS105E-200) which in Germany already is end-of-life
- GS105Ev1 (which is unmanaged and cannot do port-mirroring and is confusingly sold as GS105E-100) which is end-of-life but still sold
Via [Wayback/Archive] Everyone Should Have One of These – EASY Packet Capture! – YouTube who explains very well why you need a switch that can do port-mirroring, then recommends the GS105E but forgets to mention:
- there are different revisions of the GS105E with the above drawbacks
- there is GS305E
Related:
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Posted in Blue team, Communications Development, Development, Ethernet, Hardware, Internet protocol suite, Network-and-equipment, Power User, Red team, Security, Software Development, TCP, UDP | Leave a Comment »
html – What can cause Chrome to give an net::ERR_FAILED on cached content against a server on localhost? – Stack Overflow
Posted by jpluimers on 2025/08/07
On my research list [Wayback/Archive] html – What can cause Chrome to give an net::ERR_FAILED on cached content against a server on localhost? – Stack Overflow
The reason what that back then this would fail (but worked in Firefox and Safari, and because I was in a hurry I didn’t research further): [Wayback/Archive] https://www.office.com/
This site can’t be reached
The webpage at https://www.office.com/ might be temporarily down or it may have moved permanently to a new web address.
ERR_FAILED
Thanks [Wayback/Archive] Mason Wheeler and [Wayback/Archive] Joel Davey.
Details:
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Posted in Chrome, Communications Development, Development, Encryption, HTTP, https, HTTPS/TLS security, Power User, Security, TCP, TLS, Web Browsers, Web Development | Leave a Comment »
linux – Get final URL after curl is redirected – Stack Overflow (plus some Twitter scraping tricks)
Posted by jpluimers on 2025/08/06
Sometimes I need [Wayback/Archive] Redirect Checker | Check your Statuscode 301 vs 302 on the command-line, so cURL to the rescue: [Wayback/Archive] linux – Get final URL after curl is redirected – Stack Overflow. The relevant portions of answers and comments further below.
TL;DR:
Since I prefer verbose command-line arguments (you can find them at the [Wayback/Archive] curl – How To Use on-line man page) especially in scripts this HTTP GET request is what works with Twitter:
% curl --location --silent --output /dev/null --write-out "%{url_effective}\n" https://twitter.com/anyuser/status/20https://x.com/anyuser/status/20
This failed (twitter dislikes HTTP HEAD requests):
% curl --head --location --silent --output /dev/null --write-out "%{url_effective}\n" https://twitter.com/anyuser/status/20https://twitter.com/anyuser/status/20
Notes
Given so many of my scripts now run on zsh, I added the new-line because of command line – Why does a cURL request return a percent sign (%) with every request in ZSH? – Stack Overflow. You can strip that bit.
Note that these do not perform client side redirects, so they do not return the ultimate originating URL https://x.com/jack/status/20 (which was the first ever Tweet on what was back then called twttr) as Twitter on the client-side overwrites window.location.href with the final URL. Similar behaviour for getting the Twitter user handle of a Twitter user ID, more on Twitter tricks below.
Tweet by TweetID trick via [Wayback/Archive] Accessing a tweet using only its ID (and without the Twitter API) – Bram.us.
Further reading (thanks [Wayback/Archive] vise, [Wayback/Archive] Daniel Stenberg, [Wayback/Archive] Ivan, [Wayback/Archive] AndrewF, [Wayback/Archive] Roger Campanera, and [Wayback/Archive] Dave Baird):
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Posted in *nix, *nix-tools, bash, Batch-Files, Bookmarklet, Communications Development, Conference Topics, Conferences, CSS, cURL, Development, Event, HTTP, Internet protocol suite, JavaScript/ECMAScript, Power User, Scripting, SocialMedia, Software Development, TCP, Twitter, Web Browsers, Web Development | Tagged: 76 | Leave a Comment »
Tribal Knowledge? Getting the public keys from github and gitlab users from their username
Posted by jpluimers on 2025/04/03
Learned a while ago: if you have the username from a GitHub or GitLab user, you can download interesting that sometimes can make life easier (but not necessarily more secure):
github.com/username.keysgives you their public SSH keysgitlab.com/username.keysgives you their public SSH keysgithub.com/username.pnggives you their profile image
And that there are tools like gh, glab and age that can make direct use of them.
I love Twitter, so thanks for these for teaching me these little tricks:
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Posted in *nix, *nix-tools, ArchiveTeamWarrior, Conference Topics, Conferences, Development, Event, GitHub, GitLab, Internet, InternetArchive, OpenSSH, Power User, Software Development, Source Code Management, SSH, ssh/sshd, WayBack machine | Tagged: GitHub, GitLab | Leave a Comment »
Some HTTP redirect checking sites compared
Posted by jpluimers on 2025/04/02
Every now and then I want to check how a URL redirect, for instance when checking out why a domain failed loading in browsers a while ago because of certificate problems:
- [Wayback/Archive] SSL Server Test: vems-sassenheim.nl (Powered by Qualys SSL Labs)
- [Wayback/Archive] SSL Server Test: www.vems-sassenheim.nl (Powered by Qualys SSL Labs)
The thing was that back then, the site officially did not have a security certificate, but somehow the provider had installed a self-signed one. Most web-browsers then auto-redirect from http to https. Luckily the archival sites can archive without redirecting:
When querying [Wayback/Archive] redirect check – Google Search, you get quite some results. These are the ones I use most in descending order of preference and why they are at that position:
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Posted in *nix, *nix-tools, archive.is / archive.today, Communications Development, Development, Encryption, HTTP, https, HTTPS/TLS security, Internet, Internet protocol suite, ISP, Power User, Security, Software Development, TCP, WayBack machine, Web Development, wget, xs4all | Leave a Comment »
The Wiert Corner - irregular stream of stuff 