Keep a published rule when some invitation emails already went out, and only set Reply-To when the inviter address is a mailbox.

lib/server/ruleStakeholderInviteMail.ts

@@ -8,6 +8,28 @@ import {
 
 export const RULE_STAKEHOLDER_INVITE_LOGO_PATH = getAssetPath(ASSETS.LOGO_MARK);
 
+/** Letter name when neither the inviter nor the rule owner has an email. */
+export const RULE_STAKEHOLDER_INVITER_FALLBACK = "Someone from this community";
+
+const MAILBOX_PATTERN = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+
+/** Reply-To only when the inviter value is a mailbox. */
+export function stakeholderInviteReplyTo(
+  inviterEmail: string,
+): string | undefined {
+  const mailbox = inviterEmail.trim().toLowerCase();
+  if (!MAILBOX_PATTERN.test(mailbox)) return undefined;
+  return mailbox;
+}
+
+/** Email addresses stay lowercase; any other label is kept for the letter. */
+export function stakeholderInviteInviterLabel(inviterEmail: string): string {
+  const replyTo = stakeholderInviteReplyTo(inviterEmail);
+  if (replyTo) return replyTo;
+  const trimmed = inviterEmail.trim();
+  return trimmed.length > 0 ? trimmed : RULE_STAKEHOLDER_INVITER_FALLBACK;
+}
+
 const PREVIEW_TEXT =
   "It covers how they talk, who belongs, how they decide and what happens when they disagree.";
 
@@ -44,7 +66,7 @@ export function buildRuleStakeholderInviteMail(
   input: RuleStakeholderInviteMailInput,
 ): RuleStakeholderInviteMailContent {
   const communityName = input.communityName.trim() || "A community";
-  const inviterEmail = input.inviterEmail.trim().toLowerCase();
+  const inviterEmail = stakeholderInviteInviterLabel(input.inviterEmail);
   const origin = input.origin.replace(/\/$/, "");
   const verifyUrl = input.verifyUrl;
   const copyUrl = ruleStakeholderInviteCopyUrl(verifyUrl);