Action Mailer InlinePreviewInterceptor

Implements a mailer preview interceptor that converts image tag src attributes that use inline cid: style URLs to data: style URLs so that they are visible when previewing an HTML email in a web browser.

This interceptor is enabled by default. To disable it, delete it from the ActionMailer::Base.preview_interceptors array:

ActionMailer::Base.preview_interceptors.delete(ActionMailer::InlinePreviewInterceptor)