outbound.qs.icloud.com is holding my messages for 15 to 25 minutes before delivering them

Starting this morning (at least since 15:20 UTC on 4 June 2025), outbound.qs.icloud.com (with a public IP address) has been holding my messages for 15 to 25 minutes before passing them on to the next server. This applies to sending from MacOS Mail, iOS Mail, and iPadOS Mail, but not from iCloud.com/Mail, which uses server outbound.ms.icloud.com (with a private IP address). These SMTP servers are of course server clusters, so it may simply be that my account is being routed to the same problem server, since it happens from both my home network and the mobile network for my phone when not on WiFi.

Here are mail headers showing the delay for an example:

Received: from p00-icloudmta-asmtp-us-east-2d-20-percent-0 by p139-mailgateway-smtp-5ddf777dd4-qcs49 (mailgateway 2520B69) with SMTP id 10341ef2-7cdb-4703-98bc-30f58eb1c445  for <********@icloud.com>; Wed, 4 Jun 2025 16:58:36 GMT

Received: from outbound.qs.icloud.com (localhost [127.0.0.1]) by *******.icloud.com (Postfix) with ESMTPS id 6300E1802F82; Wed,  4 Jun 2025 16:58:33 +0000 (UTC)

Received: from apple (*********.me.com [17.57.155.37]) by outbound.qs.icloud.com (Postfix) with ESMTPSA id 1264318034FB; Wed,  4 Jun 2025 16:42:10 +0000 (UTC)

[Edited by Moderator]