EdHosting Posted February 23, 2004 Posted February 23, 2004 To be specific, if you change the MX record for a domain hosted at TCH, the change is immediate with TCH's DNS servers, but it may take several hours or more for SMTP email servers to use the new pointer. This is not a TCH problem, it's the way that the DNS system was designed to work. Whenever an SMTP mail server attempts to deliver mail to a TCH hosted domain, it (or more specifically it's own DNS server) first checks it's local DNS cache. If an MX record for the domain is found in the cache, it uses it to deliver the mail to the SMTP server that the MX record points to. Otherwise, it asks the TCH DNS server for the MX record and adds it to the local cache. Once the MX record is in the local cache, it remains active for a period of time called "Time To Live". I believe the default TTL value is 4 hours, but can be forced higher by Sys Admins. I found this out while transitioning email for a couple of TCH hosted domains to a dedicated in-house Email server. I did this by reconfiguring each Outlook client to use the new email server and then deleting the user's mailbox on the TCH server and replacing it with a manual forwarding entry. After the last client had been reconfigured, it was time to change the MX record so that all email for the domain(s) would be redirected to the new email server and the individual forwarding entries would no longer be needed. I did this using cPanel and it reported that the change had been made. But in a "Senior Moment", I went ahead and deleted all the manual forwarding entries. As a final check, I tried sending some test messages to myself from a remote Outlook client, but they didn't go through. After a lot of testing and checking, I opened up a trouble ticket. But the response I got from them was "the MX record is fine, it should be working". Now, although this was true, someone should have mentioned this TTL caching issue to me. Instead, I had to figure it out myself. Hopefully, TCH Support will pick up on this for future reference. So the bottom line is, if you change the MX record on the TCH server, you should plan on waiting a day or so before you delete the user's mailboxes or any individual forwarding entries. Quote
MikeJ Posted February 23, 2004 Posted February 23, 2004 Just for the record, due to the distributed nature of DNS, any change is not guaranteed to be immediate (and most likely will take hours to a couple days to propagate). This includes MX records, name server records, host records, etc... Quote
EdHosting Posted February 23, 2004 Author Posted February 23, 2004 This wasn't a propagation issue. MX records don't propagate. Propagation of DNS refers to the hierarchal distribution and updating of the authoritative name servers for all the domains in the Internet. Changing the name servers for a given domain can, and often does take several days to propagate. Normally, this kind of change occurs when you change hosting providers. Changing the MX record does not change name server for the domain. But caching name servers may take several hours before re-querying those name servers for a fresh resolution of the MX record. I agree that in the end the result is the same. Any changes to DNS will require a period of time before they resolve properly everywhere. Quote
MikeJ Posted February 23, 2004 Posted February 23, 2004 Well, you're splitting hairs on my use of propagate. I meant it as in the change propagating (spreading) through the various DNS caches. Probably a bad choice in wording on my part as most people do usually refer to propagate in the sense of items that update the root servers. Quote
EdHosting Posted February 23, 2004 Author Posted February 23, 2004 .... Probably a bad choice in wording on my part ... Just wanted to make sure that others who read this topic don't propagate that. Quote
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