diff --git a/lib/validators/constants.rb b/lib/validators/constants.rb
index db1d1b9..90d49f8 100644
--- a/lib/validators/constants.rb
+++ b/lib/validators/constants.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 module Validators
-  EMAIL_FORMAT = /\A[a-z0-9]+([-._][a-z0-9]+)*(\+[^@]+)?@[a-z0-9]+([.-][a-z0-9]+)*\.[a-z]{2,}\z/i.freeze
+  EMAIL_FORMAT = /\A[a-z0-9]+([-._][a-z0-9]+)*_?(\+[^@]+)?@[a-z0-9]+([.-][a-z0-9]+)*\.[a-z]{2,}\z/i.freeze
   MICROSOFT_EMAIL_FORMAT = /\A[a-z0-9][a-z0-9._-]*[a-z0-9_-]+(\+[a-z0-9]+)?@(hotmail|outlook).com\z/i.freeze
 
   # Source: https://github.com/henrik/validates_url_format_of
diff --git a/test/support/emails.rb b/test/support/emails.rb
index e99f480..2565e76 100644
--- a/test/support/emails.rb
+++ b/test/support/emails.rb
@@ -30,6 +30,7 @@
 
 VALID_EMAILS = [
   "valid@somedomain.com",
+  "valid_@somedomain.com",
   "Valid@test.somedomain.com",
   "valid+valid123@test.somedomain.com",
   "valid_valid123@test.somedomain.com",