I recently started using CloudFlare and am having a few teething problems.
Our domain is netlanguages.com and while we have a lot of sub-domains listen, we are currently only trialling a few of
the servers through
the CloudFlare CDN (for example, www.netlanguages.com is enabled for CDN, netlanguages.com is not).
The actual CDN service seems to be reliable, but
the problem that we are having is with DNS, and specifically with mail delivery.
The background is that we have contact forms on our web site which use PHP mail() to send
the details to end-users' email addresses, with
the "from" address of
the messages being
[email protected] which is a valid address on our mail server. Most of
the mails are arriving correctly, but a few specific people are not receiving them.
The webserver uses qmail to deliver
the messages, and
the qmail log files show us some of
the errors that
the receiving mail servers return when they reject
the mail delivery attempt. Two examples:
Connected to 94.100.176.20 but sender was rejected./Remote host said: 421 DNS problem (interdominios.netlanguages.com). Try again later
Connected to 213.186.33.29 but sender was rejected./Remote host said: 451 DNS temporary failure (#4.3.0)
From what I can tell,
the receiving SMTP server is doing a DNS lookup of some description on either
the host of
the "from" email address (netlanguages.com) or
the server name given in
the EHLO command of
the SMTP conversation (in
the first example
above, interdominios.netlanguages.com), both of which should resolve to non-CloudFlare IP addresses.
I've read that
the CloudFlare DNS service is very reliable and fast but both of
the problems
above seem to point to a problem with remote servers unable to do DNS lookups.
I should also point out that we changed our DNS to CloudFlare on 6th Feb, and since then started experiencing these mail delivery problems. On 22nd Feb we moved our DNS away from CloudFlare to see if
the issues were related to CloudFlare and after a few hours delivery began to work. Then on 26th Feb I moved
the DNS back to CloudFlare again and delivery problems started again.
The issues definitely seems to be related to DNS, but I don't know if it's a configuration issue, or something else.
Finally, I should say that our two DNS MX records point to non-CDN A record IP addresses, interdominios.netlanguages.com (the web and qmail server) also points to a non-CDN A record IP address.
Does anyone know what
the problem could be here? Any light you can shed on this will be most appreciated.
Many thanks,
Andy