Curl Error 56 Failure when receiving data from the peer

Hi
I am using MailPoet to send a monthly (or so) newsletter to under 200 subscribers for a small, non-profit organsation. Because of the nature of the business, budget is very tight and we do not have many options for using premium services. Our site is hosted on Heart Internet who never allow loopbacks to run.

A while back I was using a free third party SMTP service to send the emails, because sending through our own mail server was causing too many bounces and emails ending up in Spam folders. A few months ago, I noticed that MailPoet was offering a sending service and so, post pandemic, I was delighted to change to this and send out an email without any problems. Fixed, I thought.

However, this months newsletter was prepared and the preview successfully sent to me and one other, but when I tried to send the email to recipients, it would not go, citing Curl error 56 Failure when receiving data from the peer.

A new error to me, I contacted my host, who simply reiterated that they don’t allow loopback connections. However, very soon after, it did go, as did the subsequent newsletter after showing the same error initially.

Please can anyone help me understand why it went correctly the first time around (previous version) and why, after showing as failing to send, it then sent successfully? This isn’t an error I’d seen before relating to loopback connections being disallowed on Heart’s servers. They don’t seem willing to help me get what’s happening, just telling me that if I want to run loopbacks, I need to come off shared servers. For this organisation, that isn’t a viable option.

Thanks so much for any help.

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