LetterOpenerWeb::Redis

Redis storage backend for letter_opener_web.

This gem allows you to store email letters and attachments in Redis instead of the local filesystem, enabling multi-instance deployments and shared email viewing across application servers.

Add these lines to your application's Gemfile:

gem 'letter_opener_web'
gem 'letter_opener_web-redis', require: 'letter_opener_web_redis'

Set up your Redis connection in your Rails configuration file (e.g., config/environments/development.rb):

# Require the gem first
require 'letter_opener_web_redis'

LetterOpenerWeb.configure do |config|
  # Use the Redis storage backend
  config.letter_class = LetterOpenerWeb::RedisLetter

  # Redis Configuration
  config.redis_url = ENV.fetch('REDIS_URL', 'redis://localhost:6379/0')
  config.redis_namespace = 'letter_opener' # optional, defaults to 'letter_opener'
end

Update your ActionMailer configuration to use the Redis delivery method:

config.action_mailer.delivery_method = :letter_opener_web_redis

Emails are stored in Redis with the following key structure:

{namespace}:letters:ids                          # Set of all letter IDs
{namespace}:letter:{id}:metadata                 # JSON metadata (id, sent_at, attachments)
{namespace}:letter:{id}:plain                    # Plain text HTML
{namespace}:letter:{id}:rich                     # Rich HTML
{namespace}:letter:{id}:attachment:{filename}    # Base64-encoded attachment content

Where {namespace} defaults to letter_opener but can be customized via configuration.

Since Redis stores all data in memory, be mindful of:

• Email Size: Large attachments will consume significant memory
• Retention: Consider implementing TTL (time-to-live) for old emails
• Limits: Monitor Redis memory usage and set appropriate limits

The gem is available as open source under the terms of the MIT License.