diff --git a/config/boot.rb b/config/boot.rb
index 72ea699a5..e7d68c4ad 100644
--- a/config/boot.rb
+++ b/config/boot.rb
@@ -1,14 +1,19 @@
 # frozen_string_literal: true
 
-# Rack 3.1.14 or later limits query parameters to 4096 by default, which
-# prevents saving workflows with many statuses.
-# Setting RACK_QUERY_PARSER_PARAMS_LIMIT to 65536 allows handling up to
-# approximately 100 statuses.
+# Rack 3.1.14 or later sets default limits of 4MB for query string bytesize
+# and 4096 for the number of query parameters. These limits are too low
+# for Redmine and can cause the following issues:
+#
+# - The low bytesize limit prevents the mail handler from processing incoming
+#   emails larger than 4MB (https://www.redmine.org/issues/42962)
+# - The low parameter limit prevents saving workflows with many statuses
+#   (https://www.redmine.org/issues/42875)
 #
 # See also:
-# - https://www.redmine.org/issues/42875
 # - https://github.com/rack/rack/blob/v3.1.16/README.md#configuration
+# - https://github.com/rack/rack/blob/v3.1.16/lib/rack/query_parser.rb#L54
 # - https://github.com/rack/rack/blob/v3.1.16/lib/rack/query_parser.rb#L57
+ENV['RACK_QUERY_PARSER_BYTESIZE_LIMIT'] ||= '33554432'
 ENV['RACK_QUERY_PARSER_PARAMS_LIMIT'] ||= '65536'
 
 # Set up gems listed in the Gemfile.