diff --git a/app/models/credential.rb b/app/models/credential.rb
index 1af484d..2c37593 100644
--- a/app/models/credential.rb
+++ b/app/models/credential.rb
@@ -23,7 +23,7 @@ class Credential < ApplicationRecord
 
   belongs_to :server
 
-  TYPES = ["SMTP", "API", "SMTP-IP"]
+  TYPES = ["SMTP", "API", "SMTP-IP"].freeze
 
   validates :key, presence: true, uniqueness: { case_sensitive: false }
   validates :type, inclusion: { in: TYPES }
diff --git a/app/models/domain.rb b/app/models/domain.rb
index ae0b416..ba61992 100644
--- a/app/models/domain.rb
+++ b/app/models/domain.rb
@@ -44,15 +44,14 @@ class Domain < ApplicationRecord
 
   include HasDNSChecks
 
-  VERIFICATION_EMAIL_ALIASES = ["webmaster", "postmaster", "admin", "administrator", "hostmaster"]
+  VERIFICATION_EMAIL_ALIASES = ["webmaster", "postmaster", "admin", "administrator", "hostmaster"].freeze
+  VERIFICATION_METHODS = ["DNS", "Email"].freeze
 
   belongs_to :server, optional: true
   belongs_to :owner, optional: true, polymorphic: true
   has_many :routes, dependent: :destroy
   has_many :track_domains, dependent: :destroy
 
-  VERIFICATION_METHODS = ["DNS", "Email"]
-
   validates :name, presence: true, format: { with: /\A[a-z0-9\-.]*\z/ }, uniqueness: { case_sensitive: false, scope: [:owner_type, :owner_id], message: "is already added" }
   validates :verification_method, inclusion: { in: VERIFICATION_METHODS }
 
diff --git a/app/models/http_endpoint.rb b/app/models/http_endpoint.rb
index a2e2faa..ff33a24 100644
--- a/app/models/http_endpoint.rb
+++ b/app/models/http_endpoint.rb
@@ -31,8 +31,8 @@ class HTTPEndpoint < ApplicationRecord
   has_many :routes, as: :endpoint
   has_many :additional_route_endpoints, dependent: :destroy, as: :endpoint
 
-  ENCODINGS = ["BodyAsJSON", "FormData"]
-  FORMATS = ["Hash", "RawMessage"]
+  ENCODINGS = ["BodyAsJSON", "FormData"].freeze
+  FORMATS = ["Hash", "RawMessage"].freeze
 
   before_destroy :update_routes
 
diff --git a/app/models/organization.rb b/app/models/organization.rb
index 0857822..57e16cd 100644
--- a/app/models/organization.rb
+++ b/app/models/organization.rb
@@ -25,7 +25,7 @@
 
 class Organization < ApplicationRecord
 
-  RESERVED_PERMALINKS = ["new", "edit", "remove", "delete", "destroy", "admin", "mail", "org", "server"]
+  RESERVED_PERMALINKS = ["new", "edit", "remove", "delete", "destroy", "admin", "mail", "org", "server"].freeze
 
   INITIAL_QUOTA = 10
   INITIAL_SUPER_QUOTA = 10_000
diff --git a/app/models/route.rb b/app/models/route.rb
index 0561551..cd837d0 100644
--- a/app/models/route.rb
+++ b/app/models/route.rb
@@ -24,7 +24,9 @@
 
 class Route < ApplicationRecord
 
-  MODES = ["Endpoint", "Accept", "Hold", "Bounce", "Reject"]
+  MODES = ["Endpoint", "Accept", "Hold", "Bounce", "Reject"].freeze
+  SPAM_MODES = ["Mark", "Quarantine", "Fail"].freeze
+  ENDPOINT_TYPES = ["SMTPEndpoint", "HTTPEndpoint", "AddressEndpoint"].freeze
 
   include HasUUID
 
@@ -33,9 +35,6 @@ class Route < ApplicationRecord
   belongs_to :endpoint, polymorphic: true, optional: true
   has_many :additional_route_endpoints, dependent: :destroy
 
-  SPAM_MODES = ["Mark", "Quarantine", "Fail"]
-  ENDPOINT_TYPES = ["SMTPEndpoint", "HTTPEndpoint", "AddressEndpoint"]
-
   validates :name, presence: true, format: /\A(([a-z0-9\-.]*)|(\*)|(__returnpath__))\z/
   validates :spam_mode, inclusion: { in: SPAM_MODES }
   validates :endpoint, presence: { if: proc { mode == "Endpoint" } }
diff --git a/app/models/server.rb b/app/models/server.rb
index 33a72ca..c2f39a6 100644
--- a/app/models/server.rb
+++ b/app/models/server.rb
@@ -43,7 +43,8 @@
 
 class Server < ApplicationRecord
 
-  RESERVED_PERMALINKS = ["new", "all", "search", "stats", "edit", "manage", "delete", "destroy", "remove"]
+  RESERVED_PERMALINKS = ["new", "all", "search", "stats", "edit", "manage", "delete", "destroy", "remove"].freeze
+  MODES = ["Live", "Development"].freeze
 
   include HasUUID
   include HasSoftDestroy
@@ -64,8 +65,6 @@ class Server < ApplicationRecord
   has_many :track_domains, dependent: :destroy
   has_many :ip_pool_rules, dependent: :destroy, as: :owner
 
-  MODES = ["Live", "Development"]
-
   random_string :token, type: :chars, length: 6, unique: true, upper_letters_only: true
   default_value :permalink, -> { name ? name.parameterize : nil }
   default_value :raw_message_retention_days, -> { 30 }
diff --git a/app/models/smtp_endpoint.rb b/app/models/smtp_endpoint.rb
index cda9dac..84c40aa 100644
--- a/app/models/smtp_endpoint.rb
+++ b/app/models/smtp_endpoint.rb
@@ -26,7 +26,7 @@ class SMTPEndpoint < ApplicationRecord
   has_many :routes, as: :endpoint
   has_many :additional_route_endpoints, dependent: :destroy, as: :endpoint
 
-  SSL_MODES = ["None", "Auto", "STARTTLS", "TLS"]
+  SSL_MODES = ["None", "Auto", "STARTTLS", "TLS"].freeze
 
   before_destroy :update_routes
 
diff --git a/app/models/webhook_event.rb b/app/models/webhook_event.rb
index a0a2236..a54da56 100644
--- a/app/models/webhook_event.rb
+++ b/app/models/webhook_event.rb
@@ -25,7 +25,7 @@ class WebhookEvent < ApplicationRecord
     "MessageLinkClicked",
     "MessageLoaded",
     "DomainDNSError"
-  ]
+  ].freeze
 
   belongs_to :webhook
 
diff --git a/app/models/webhook_request.rb b/app/models/webhook_request.rb
index 567c1bb..97d4b6f 100644
--- a/app/models/webhook_request.rb
+++ b/app/models/webhook_request.rb
@@ -21,7 +21,7 @@ class WebhookRequest < ApplicationRecord
 
   include HasUUID
 
-  RETRIES = { 1 => 2.minutes, 2 => 3.minutes, 3 => 6.minutes, 4 => 10.minutes, 5 => 15.minutes }
+  RETRIES = { 1 => 2.minutes, 2 => 3.minutes, 3 => 6.minutes, 4 => 10.minutes, 5 => 15.minutes }.freeze
 
   belongs_to :server
   belongs_to :webhook, optional: true
diff --git a/lib/postal/app_logger.rb b/lib/postal/app_logger.rb
index 98c6fa2..13fd044 100644
--- a/lib/postal/app_logger.rb
+++ b/lib/postal/app_logger.rb
@@ -45,8 +45,8 @@ module Postal
 
   class LogFormatter
 
-    TIME_FORMAT = "%Y-%m-%dT%H:%M:%S.%3N".freeze
-    COLORS = [32, 34, 35, 31, 32, 33]
+    TIME_FORMAT = "%Y-%m-%dT%H:%M:%S.%3N"
+    COLORS = [32, 34, 35, 31, 32, 33].freeze
 
     def call(severity, datetime, progname, msg)
       time = datetime.strftime(TIME_FORMAT)
diff --git a/lib/postal/message_db/statistics.rb b/lib/postal/message_db/statistics.rb
index 723a61c..d069bd2 100644
--- a/lib/postal/message_db/statistics.rb
+++ b/lib/postal/message_db/statistics.rb
@@ -8,8 +8,8 @@ module Postal
         @database = database
       end
 
-      STATS_GAPS = { hourly: :hour, daily: :day, monthly: :month, yearly: :year }
-      COUNTERS = [:incoming, :outgoing, :spam, :bounces, :held]
+      STATS_GAPS = { hourly: :hour, daily: :day, monthly: :month, yearly: :year }.freeze
+      COUNTERS = [:incoming, :outgoing, :spam, :bounces, :held].freeze
 
       #
       # Increment an appropriate counter
diff --git a/lib/postal/message_inspectors/spam_assassin.rb b/lib/postal/message_inspectors/spam_assassin.rb
index 24395e1..c3346bb 100644
--- a/lib/postal/message_inspectors/spam_assassin.rb
+++ b/lib/postal/message_inspectors/spam_assassin.rb
@@ -7,7 +7,7 @@ module Postal
       EXCLUSIONS = {
         outgoing: ["NO_RECEIVED", "NO_RELAYS", "ALL_TRUSTED", "FREEMAIL_FORGED_REPLYTO", "RDNS_DYNAMIC", "CK_HELO_GENERIC", /^SPF_/, /^HELO_/, /DKIM_/, /^RCVD_IN_/],
         incoming: []
-      }
+      }.freeze
 
       def inspect_message(inspection)
         data = nil
diff --git a/lib/postal/received_header.rb b/lib/postal/received_header.rb
index a3fe372..a9bec15 100644
--- a/lib/postal/received_header.rb
+++ b/lib/postal/received_header.rb
@@ -6,7 +6,7 @@ module Postal
     OUR_HOSTNAMES = {
       smtp: Postal.config.dns.smtp_server_hostname,
       http: Postal.config.web.host
-    }
+    }.freeze
 
     class << self
 
diff --git a/lib/postal/reply_separator.rb b/lib/postal/reply_separator.rb
index 9f6d416..30726bd 100644
--- a/lib/postal/reply_separator.rb
+++ b/lib/postal/reply_separator.rb
@@ -15,7 +15,7 @@ module Postal
       /^>*\s*Sent from my.*/m,
       /^>*\s*=== Please reply above this line ===.*/m,
       /(^>.*\n?){10,}/
-    ]
+    ].freeze
 
     def self.separate(text)
       return "" unless text.is_a?(String)