From e2cb83ce28353836e7daa96bdfd93067687f6daa Mon Sep 17 00:00:00 2001
From: Richard Schreiber <schreiber@pretix.eu>
Date: Wed, 11 Feb 2026 12:00:54 +0100
Subject: [PATCH] Fix marking invoices transmitted for emails with uppercase
 letters (#5885)

---
 src/pretix/base/services/mail.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/pretix/base/services/mail.py b/src/pretix/base/services/mail.py
index 15b09867b8..2615660a48 100644
--- a/src/pretix/base/services/mail.py
+++ b/src/pretix/base/services/mail.py
@@ -519,6 +519,7 @@ def mail_send_task(self, **kwargs) -> bool:
                             )
                         except InvoiceAddress.DoesNotExist:
                             pass
+                        expected_recipients = {e.lower() for e in expected_recipients if e}
                         if any(t in expected_recipients for t in outgoing_mail.to):
                             invoices_to_mark_transmitted.append(inv)