diff --git a/backend/LexBoxApi/Services/EmailService.cs b/backend/LexBoxApi/Services/EmailService.cs
index b1a11a77c..2e8ce7b52 100644
--- a/backend/LexBoxApi/Services/EmailService.cs
+++ b/backend/LexBoxApi/Services/EmailService.cs
@@ -217,7 +217,8 @@ await RenderEmail(email,
     }
     public async Task SendUserAddedEmail(User user, string projectName, string projectCode)
     {
-        var email = StartUserEmail(user) ?? throw new ArgumentNullException("emailAddress");
+        var email = StartUserEmail(user);
+        if (email is null) return; // Guest users have no email address, so we won't notify them by email and that's not an error
         await RenderEmail(email, new UserAddedEmail(user.Name, user.Email!, projectName, projectCode), user.LocalizationCode);
         await SendEmailWithRetriesAsync(email);
     }