DNS/SMTP transport modes don't work

It works for me. Perhaps you are using a different version of symfony - or even a mixture of incompatible versions?

Also get this error when trying to add a DSN transport type. symfony/http-client v6.4.6 is installed.

@adamps when you say "It works for me", what version of symfony/http-client are you using?

Here is a dump from my `composer show` for all packages match drupal/core* or symfony/*

drupal/core                                    10.3.5        Drupal is an open source content management platform powering millions of websites and applications.
drupal/core-composer-scaffold                  10.3.5        A flexible Composer project scaffold builder.
drupal/core-dev                                10.3.2        require-dev dependencies from drupal/drupal; use in addition to drupal/core-recommended to run tests from drupal/core.
drupal/core-recommended                        10.3.5        Core and its dependencies with known-compatible minor versions. Require this project INSTEAD OF drupal/core.
drupal/core-vendor-hardening                   10.3.5        Hardens the vendor directory for when it's in the docroot.
symfony/browser-kit                            6.4.8         Simulates the behavior of a web browser, allowing you to make requests, click on links and submit forms programmatically
symfony/console                                6.4.12        Eases the creation of beautiful and testable command line interfaces
symfony/css-selector                           6.4.8         Converts CSS selectors to XPath expressions
symfony/dependency-injection                   6.4.10        Allows you to standardize and centralize the way objects are constructed in your application
symfony/deprecation-contracts                  3.5.0         A generic function and convention to trigger deprecation notices
symfony/dom-crawler                            6.4.12        Eases DOM navigation for HTML and XML documents
symfony/error-handler                          6.4.10        Provides tools to manage errors and ease debugging PHP code
symfony/event-dispatcher                       6.4.8         Provides tools that allow your application components to communicate with each other by dispatching events and listening to them
symfony/event-dispatcher-contracts             3.5.0         Generic abstractions related to dispatching event
symfony/filesystem                             6.4.12        Provides basic utilities for the filesystem
symfony/finder                                 6.4.11        Finds files and directories via an intuitive fluent interface
symfony/http-foundation                        6.4.10        Defines an object-oriented layer for the HTTP specification
symfony/http-kernel                            6.4.10        Provides a structured process for converting a Request into a Response
symfony/lock                                   6.4.8         Creates and manages locks, a mechanism to provide exclusive access to a shared resource
symfony/mailer                                 6.4.9         Helps sending emails
symfony/mime                                   6.4.9         Allows manipulating MIME messages
symfony/phpunit-bridge                         6.4.11        Provides utilities for PHPUnit, especially user deprecation notices management
symfony/polyfill-ctype                         1.29.0        Symfony polyfill for ctype functions
symfony/polyfill-iconv                         1.29.0        Symfony polyfill for the Iconv extension
symfony/polyfill-intl-grapheme                 1.29.0        Symfony polyfill for intl's grapheme_* functions
symfony/polyfill-intl-idn                      1.29.0        Symfony polyfill for intl's idn_to_ascii and idn_to_utf8 functions
symfony/polyfill-intl-normalizer               1.29.0        Symfony polyfill for intl's Normalizer class and related functions
symfony/polyfill-mbstring                      1.29.0        Symfony polyfill for the Mbstring extension
symfony/polyfill-php72                         1.31.0        Symfony polyfill backporting some PHP 7.2+ features to lower PHP versions
symfony/polyfill-php73                         1.31.0        Symfony polyfill backporting some PHP 7.3+ features to lower PHP versions
symfony/polyfill-php80                         1.31.0        Symfony polyfill backporting some PHP 8.0+ features to lower PHP versions
symfony/polyfill-php81                         1.31.0        Symfony polyfill backporting some PHP 8.1+ features to lower PHP versions
symfony/polyfill-php82                         1.31.0        Symfony polyfill backporting some PHP 8.2+ features to lower PHP versions
symfony/polyfill-php83                         1.29.0        Symfony polyfill backporting some PHP 8.3+ features to lower PHP versions
symfony/process                                6.4.12        Executes commands in sub-processes
symfony/psr-http-message-bridge                6.4.10        PSR HTTP message bridge
symfony/routing                                6.4.10        Maps an HTTP request to a set of configuration variables
symfony/serializer                             6.4.10        Handles serializing and deserializing data structures, including object graphs, into array structures or other formats like XML and JSON.
symfony/service-contracts                      3.5.0         Generic abstractions related to writing services
symfony/string                                 6.4.12        Provides an object-oriented API to strings and deals with bytes, UTF-8 code points and grapheme clusters in a unified way
symfony/translation-contracts                  3.5.0         Generic abstractions related to translation
symfony/validator                              6.4.10        Provides tools to validate values
symfony/var-dumper                             6.4.11        Provides mechanisms for walking through any arbitrary PHP variable
symfony/var-exporter                           6.4.9         Allows exporting any serializable PHP data structure to plain PHP code
symfony/yaml                                   6.4.12        Loads and dumps YAML files

I don't have symfony/http-client installed

I also have multiple environments missing symfony/http-client, which becomes a problem when adding a new transport type.

@adamps Could you run `composer why symfony/http-client` to see what requires the package in your setup?

I think you might have misread #5😃. Nothing requires the package for me - it is not installed. Yet I can add a new transport without any problems.

I ran into this issue this morning on a new site build on a specific device, but was unable to reproduce it using a separate computer. What ultimately fixed it after a few hours of going crazy was restarting PHP. Perhaps the opcache/apcu cache needed to be purged for it to find the HttpClient class.

Hello,

I am trying to install a new DSN transport for Mailjet. I have installed the Mailjet dependency for Symfony Mailer.
But now, when I want to create this new transport DSN via the interface '/admin/config/system/mailer/transport/add/dsn' I get an error symfony/httpclient not found. However I have installed via composer this new dependency.

How can I solve my problem? Should I configure in the settings.php this new DSN?

Thank you for your help.