GMail refusing e-mails when Cloudflare is active

Starting November, every e-mail that I send to GMail, with Cloudflare active, issues the following error (example):

[email protected]
    host []
    SMTP error from remote mail server after end of data:
    552-5.7.0 This message was blocked because its content presents a potential
    552-5.7.0 security issue. Please visit
    552-5.7.0 `

If I turn off Cloudflare, I have zero problems with the same e-mails.

Anyone facing the same issue? Any suggestions on how to fix it?

That error message you have there, is Google rejecting your message.

As indicated on the link, it would for example happen due to various types of attachments, such as e.g. various script or executable files (e.g. .exe, .bat, et al).

But it can also be because there is a link to some bad files (e.g. viruses) in the message, or otherwise content, that Google believes is bad.

Go through the contents of the actual email message being rejected, as there is something that Google doesn’t like in it.

But it could be anything, including, but not necessarily limited to things, such as e.g.:

  • Attachment(s)
  • Image(s)
  • Link(s)

It’s impossible to give any further advice, without having the full (and unedited) message at hand.

As I’ve said, this GMail error only occurs with Cloudflare activated. It started at the beginning of this month. Before that, I used Cloudflare for almost an year with no problem at all.

If I deactivate Cloudflare on my site, GMail has no problems with my e-mails, they all go through to their destinataries just fine. So the contents of the e-mail (including attachments or not) per se are not causing the error.

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