Disabled overrides should not cause conflicts

Here are some facts about how this module works that we aren't able to change:

1. If your module sends emails with hook_mail(), this creates an email builder with type "contact_form".
2. If the contact module is enabled and overridden, this creates an email builder with type "contact_form".
3. It's not supported to have two email builders with the same type.

However in your case, the contact module is disabled, so it should work. The reason it doesn't is that DefaultPluginManager::findDefinitions() first calls the alter hooks (including symfony_mailer_mailer_builder_info_alter()) and then second filters out cases where the provider doesn't exist.

Automatically closed - issue fixed for 2 weeks with no activity.