Received: from mail.xfsmail.com (MAIL.XFSMAIL.com [46.32.252.200]) by mx1.messagingengine.com (Postfix) with ESMTP id 68701F20E80
X-Spam-hits: BAYES_80 2, HTML_MESSAGE 0.001, RP_MATCHES_RCVD -0.473, LANGUAGES unknown, BAYES_USED user, SA_VERSION 3.3.2
At least it used TLS on the return email:
Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com [66.111.4.28]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.xfsmail.com (Postfix) with ESMTPS id 348821446D7
And noticed the DKIM and SPF on my email:
X-Spam-Status: No, score=-2 tagged_above=-999 required=6.31 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, SPF_PASS=-0.001] autolearn=ham
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It didn't send me an SMS after signup, or appear to have any method to stop a botnet signing up few thousand accounts and going on a spamming run. It happens to us all.
I do wonder how they are planning to fund their hobby if it gets popular.
(disclaimer, I've worked for FastMail for nearly 10 years - I have a decent idea what goes into running an email service)