Update Postal information (#3464)

Update Postal link, category, language, and description

.github/PULL_REQUEST_TEMPLATE.md

@@ -23,6 +23,7 @@ To ensure your PR is dealt with swiftly please check the following:
 - [ ] Any category you are creating has the minimum requirement of 3 items.
   If not, your addition may be inserted into `Misc/Other`.
 - [ ] Any software project you are adding to the list is actively maintained.
+- [ ] Any software project you are adding has working installation instructions.
 - [ ] The pull request title is informative, unlike "Update README.md".
   Suggested titles: "Add aaa to bbb" for adding software aaa to section bbb,
   "Remove aaa from bbb" for removing, "Fix license for aaa", etc.

README.md

@@ -383,6 +383,7 @@ Simple deployment of [E-mail](https://en.wikipedia.org/wiki/Email) servers, e.g.
 - [Mailcow](https://mailcow.email/) - Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration. ([Source Code](https://github.com/mailcow/mailcow-dockerized)) `GPL-2.0` `Docker/PHP`
 - [Mailu](https://mailu.io/) - Mailu is a simple yet full-featured mail server as a set of Docker images. ([Source Code](https://github.com/Mailu/Mailu)) `MIT` `Docker/Python`
 - [Modoboa](https://modoboa.org/en/) - Modoboa is a mail hosting and management platform including a modern and simplified Web User Interface. ([Source Code](https://github.com/modoboa/modoboa)) `ISC` `Python`
+- [Postal](https://docs.postalserver.io/) - A complete and fully featured mail server for use by websites & web servers. ([Source Code](https://github.com/postalserver/postal)) `MIT` `Docker/Ruby`
 - [Simple NixOS Mailserver](https://gitlab.com/simple-nixos-mailserver/nixos-mailserver) - Complete mailserver solution leveraging the Nix Ecosystem. `GPL-3.0` `Nix`
 - [SimpleLogin](https://simplelogin.io) - Open source email alias solution to protect your email address. Comes with browser extensions and mobile apps. ([Source Code](https://github.com/simple-login/app)) `MIT` `Docker/Python`
 - [wildduck](https://wildduck.email/) - Scalable no-SPOF IMAP/POP3 mail server. ([Source Code](https://github.com/nodemailer/wildduck)) `EUPL-1.2` `Nodejs`
@@ -437,7 +438,6 @@ Simple deployment of [E-mail](https://en.wikipedia.org/wiki/Email) servers, e.g.
 - [Mailtrain](https://github.com/Mailtrain-org/mailtrain) - Self hosted newsletter application. `GPL-3.0` `Nodejs`
 - [Mautic](https://www.mautic.org/) - Mautic is marketing automation software (email, social and more). ([Source Code](https://github.com/mautic/mautic)) `GPL-3.0` `PHP`
 - [phpList](https://phplist.org) - Newsletter and email marketing with advanced management of subscribers, bounces, and plugins. ([Source Code](https://github.com/phpList/phplist3)) `AGPL-3.0` `PHP`
-- [Postal](https://postal.atech.media/) - Fully featured open source mail delivery platform for incoming and outgoing e-mail. ([Source Code](https://github.com/postalhq/postal)) `MIT` `Ruby`
 - [Postorius](https://docs.mailman3.org/projects/postorius/en/latest/) - Web user interface to access GNU Mailman. ([Source Code](https://gitlab.com/mailman/postorius/)) `GPL-3.0` `Python`
 - [Schleuder](https://schleuder.nadir.org/) - GPG-enabled mailing list manager with resending-capabilities. ([Source Code](https://0xacab.org/schleuder/schleuder/tree/master)) `GPL-3.0` `Ruby`
 - [Sympa](https://www.sympa.org/) - Mailing list manager. `GPL-2.0` `Perl`