diff --git a/src/mail.js b/src/mail.js
index 0cbc49be0..e45eff3c6 100644
--- a/src/mail.js
+++ b/src/mail.js
@@ -162,7 +162,7 @@ function validateName(name) {
     if (name.length >= 200) return new BoxError(BoxError.BAD_FIELD, 'mailbox name too long');
 
     // also need to consider valid LDAP characters here (e.g '+' is reserved)
-    if (/[^a-zA-Z0-9.-]/.test(name)) return new BoxError(BoxError.BAD_FIELD, 'mailbox name can only contain alphanumerals and dot');
+    if (/[^a-zA-Z0-9.-_]/.test(name)) return new BoxError(BoxError.BAD_FIELD, 'mailbox name can only contain alphanumerals, dot, hyphen or underscore');
 
     return null;
 }