fix: replace imap backoff db columns with redis-based exponential backoff

app/models/channel/email.rb

@@ -39,8 +39,8 @@ class Channel::Email < ApplicationRecord
   include Reauthorizable
 
   AUTHORIZATION_ERROR_THRESHOLD = 10
-  MAX_IMAP_RETRIES = 5
-  IMAP_BACKOFF_BASE_SECONDS = 60
+  IMAP_BACKOFF_MAX_INTERVAL_MINUTES = 5
+  IMAP_BACKOFF_MAX_INTERVAL_COUNT = 5
 
   # TODO: Remove guard once encryption keys become mandatory (target 3-4 releases out).
   if Chatwoot.encryption_configured?
@@ -74,25 +74,34 @@ class Channel::Email < ApplicationRecord
     imap_enabled && imap_address == 'imap.gmail.com'
   end
 
+  def imap_retry_count
+    ::Redis::Alfred.get(imap_retry_count_key).to_i
+  end
+
   def in_backoff?
-    imap_retry_after.present? && imap_retry_after > Time.current
+    val = ::Redis::Alfred.get(imap_retry_after_key)
+    val.present? && Time.zone.at(val.to_f) > Time.current
   end
 
   def apply_imap_backoff!
     new_count = imap_retry_count + 1
-    if new_count >= MAX_IMAP_RETRIES
-      update!(imap_retry_count: 0, imap_retry_after: nil)
+    max_retries = (IMAP_BACKOFF_MAX_INTERVAL_MINUTES - 1) + IMAP_BACKOFF_MAX_INTERVAL_COUNT
+
+    if new_count > max_retries
+      Rails.logger.warn "Error for email channel - #{inbox.id} exhausted backoff (#{new_count} failures), prompting reauthorization"
+      clear_imap_backoff!
       prompt_reauthorization!
     else
-      backoff_seconds = IMAP_BACKOFF_BASE_SECONDS * (2**new_count)
-      update!(imap_retry_count: new_count, imap_retry_after: backoff_seconds.seconds.from_now)
+      wait_minutes = [new_count, IMAP_BACKOFF_MAX_INTERVAL_MINUTES].min
+      ::Redis::Alfred.set(imap_retry_count_key, new_count.to_s)
+      ::Redis::Alfred.set(imap_retry_after_key, wait_minutes.minutes.from_now.to_f.to_s)
+      Rails.logger.warn "Error for email channel - #{inbox.id} backoff retry #{new_count}/#{max_retries}, next attempt in #{wait_minutes}m"
     end
   end
 
   def clear_imap_backoff!
-    return unless imap_retry_count.positive? || imap_retry_after.present?
-
-    update!(imap_retry_count: 0, imap_retry_after: nil)
+    ::Redis::Alfred.delete(imap_retry_count_key)
+    ::Redis::Alfred.delete(imap_retry_after_key)
   end
 
   private
@@ -100,4 +109,12 @@ class Channel::Email < ApplicationRecord
   def ensure_forward_to_email
     self.forward_to_email ||= "#{SecureRandom.hex}@#{account.inbound_email_domain}"
   end
+
+  def imap_retry_count_key
+    format(::Redis::Alfred::IMAP_BACKOFF_RETRY_COUNT, channel_id: id)
+  end
+
+  def imap_retry_after_key
+    format(::Redis::Alfred::IMAP_BACKOFF_RETRY_AFTER, channel_id: id)
+  end
 end

db/migrate/20260223100000_add_imap_backoff_to_channel_email.rb

@@ -1,6 +0,0 @@
-class AddImapBackoffToChannelEmail < ActiveRecord::Migration[7.1]
-  def change
-    add_column :channel_email, :imap_retry_count, :integer, default: 0, null: false
-    add_column :channel_email, :imap_retry_after, :datetime
-  end
-end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2026_02_23_100000) do
+ActiveRecord::Schema[7.1].define(version: 2026_01_30_061021) do
   # These extensions should be enabled to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pg_trgm"
@@ -442,8 +442,6 @@ ActiveRecord::Schema[7.1].define(version: 2026_02_23_100000) do
     t.jsonb "provider_config", default: {}
     t.string "provider"
     t.boolean "verified_for_sending", default: false, null: false
-    t.integer "imap_retry_count", default: 0, null: false
-    t.datetime "imap_retry_after"
     t.index ["email"], name: "index_channel_email_on_email", unique: true
     t.index ["forward_to_email"], name: "index_channel_email_on_forward_to_email", unique: true
   end

lib/redis/redis_keys.rb

@@ -52,4 +52,8 @@ module Redis::RedisKeys
 
   ## Account Email Rate Limiting
   ACCOUNT_OUTBOUND_EMAIL_COUNT_KEY = 'OUTBOUND_EMAIL_COUNT::%<account_id>d::%<date>s'.freeze
+
+  ## IMAP Backoff / Fetch Tracking (channel_email)
+  IMAP_BACKOFF_RETRY_COUNT = 'IMAP_BACKOFF:channel_email:%<channel_id>d:retry_count'.freeze
+  IMAP_BACKOFF_RETRY_AFTER = 'IMAP_BACKOFF:channel_email:%<channel_id>d:retry_after'.freeze
 end