Cloudflare is blocking the deliverability of our email to third-party apps like Outlook or Gmail. We can access the email normally from Roundcube, but since adding Cloudflare, everyone with an email on this domain is unable to receive their email outside of Roundcube.
We know that the issue is being caused by Cloudflare because when we pause Cloudflare for this domain then we start receiving mail again on the third-party apps, but when we reactive it then the mail stops being received.
Currently, Cloudflare is deactivated because we have members that need to receive their email and cannot afford disruptions. Has anyone got experience with this issue in the past?
You are suffering from a fairly common configuration mistake. You have proxied email hostnames. The Cloudflare proxy will only pass HTTP and HTTPS traffic. Other protocols such as email must use hostnames that are set to DNS Only.
This Community Tutorial should help answer additional questions.