Cloudflare Server not response with correct status

We got lots customer complain about: “repeatedly receiving lots duplicate email again and again”. I feel this error might be caused by CloudFlare. Could someone help us have a look ?

Here is the details:

  1. Since 2020-Aug-7th, we got lots customer complain they repeatedly receiving duplicate email again and again from us.
  2. We checked our AWS SES mail server, those email are sending out ok, but never get delivered. And after 840 minutes of unsuccessful retry, we will get a bounce error: (4.4.7 smtp; 550 4.4.7 Message expired: unable to deliver in 840 minutes.<421 4.4.2 Connection timed out>)
  3. We only this problem on following recipient hostname: mx1.netsolmail.net inbound.xxxx.com.netsolmail.net mx07.register.com
  4. After nslookup, I found all these host are behind same ip address: 172.65.252.97 Cloudflare, Inc. (AS13335)

To summarize:
Our emails are delivered correct from AWS to recipients, but AWS never received delivery status from recipient server. So AWS will keep retry for 840 minutes, and recipients will keep receive same duplicate email again and again.
Since this only happen on recipients behind 172.65.252.97, I guess this is somehow related to Cloudflare server status.

I am hope can find someone here give us more information about this.

Thanks,
Xiaohan

Cloudflare does not handle email, hence it cannot be a Cloudflare issue by definition.

It is slightly weird that Register and Netsol would point their hostnames to Cloudflare, but that is something you need to clarify with them. Particularly if these addresses were actually supposed to handle email (possibly Enterprise plans).

Thanks for suggestions. I will try contact them.

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