Rails mailer previews not available from spec/mailers/previews
For me, the solution was to move everything inside
myapp/test/mailers/previews/
to
myapp/spec/mailers/previews/
After doing so, the mailer previews were accessible at the usual URL:
http://localhost:3000/rails/mailers
I found this information here
Use
config.action_mailer.preview_path = "#{Rails.root}/spec/mailers/previews"
in config/environments/development.rb
to define the path where previews are located.
Since you're using RSpec, it's expected that you use the spec
folder.
It that's the case, I'd rather move your file to spec/mailers/previews/user_mailer_preview.rb