I saw this on the latest Drupal 10.0 release with a fresh installation when enabling easy_email:
Circular reference detected for service "entity_type.manager", path: "plugin.cache_clearer -> entity_type.manager -> string_translation -> string_translator.locale.lookup -> config.factory -> symfony_mailer.config_override -> plugin.manager.email_builder".
Not sure how that could be resolved. It looks to me that symfony_mailer.config_override is causing this and the path starting at plugin.cache_clearer isn't really responsible, as any service that depends on entity_type_manage could be causing this.
Closed: cannot reproduce
2.1
Code
I don't think this issue is specifically with Easy Email. I see a few similar issues in the Symfony Mailer module issue queue: https://www.drupal.org/project/issues/symfony_mailer?text=Circular+refer... →
I've also never experienced this when using Symfony Mailer Lite.