Rails 4.2 deprecates mailers from using _path helpers and from path helpers being called with only_path => false. They should all be changed to use _url helpers.
Related issues
Refactor #14006: Mailers calling *_path with :only_path => false should use _url helpers
Added by Dominic Cleal about 8 years ago
fixes #14006 - use URL helpers in mailers
Rails 4.2 deprecates mailers from using _path helpers and from path
helpers being called with only_path => false. They should all be
changed to use _url helpers.