Need explaination of how exchange routes replies to emails

Hi,
48hrs ago, I changed the mx records for my domain to point to a new A record.
Within a few hours I was receiving emails via the new mx entry into my exchange server.
I can send test emails in from domains like btopenworld.com, hotmail.com and excite.co.uk
But when I send an email from the btconnect.com domain via OWA offered by BT the email does not arrive.
If I send the email via my Outlook account from the btconnect.com domain using smtp.btconnect.com it routes into the exchange server fine.
Is this an issue with BT’s  OWA server caching my old mx record and not picking up the new old?
Can I force an update, or do I have to wait?

Also how does exchange route replies to emails?
If I reply to a email sent to my btconnect.com account via BT’s OWA it routes fine and appears in my exchange inbox. Does it use the internet headers on the mail to route the message differently and ignore the mx records?
Or do BT use a different smtp servers for sending and a different set for receiving when it comes to the OWA service?
BenthamLtdAsked:
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Hilal1924Commented:
You Said "
If I reply to a email sent to my btconnect.com account via BT’s OWA it routes fine and appears in my exchange inbox. Does it use the internet headers on the mail to route the message differently and ignore the mx records? "

===> Answer to this is that When you reply to an email, The email header will have a "reply to" field in it and it is used to route emails back to the sender. So you are right, It uses the Header Info.

MX records are Notorious for being slow on Updating and distributed via Internet. Most probably your ISP DNS allows only Authorized Zone Updates which will delay the process of Updating worldwide DNS settings for your Domain.  So it could take some time to have it refreshed all over. Though In my experience 48 hours are more than enough to get the DNS updated. Did you try sending mail via Gmail or Hotmail to the Mail Server whose MX is updated ?

Cheers,
Hilal
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tigermattCommented:

The DNS records responsible for routing mail for your domain are stored in DNS and will have a Time to Live (TTL) value associated with them. This is the length of time that record can be cached on a DNS server before the cached value is purged and the record re-requested from the authoritative name servers.

48 hours is a significant time for a TTL, but it is a plausible length of time. I would normally allow at least 48 hours in extreme cases for DNS propagation (all records to expire from caches across the world) to take place.

You cannot *easily* force an update -- the only way I can think of would have been to reduce the TTL of the record well before you changed it, so the lower TTL had already propagated to DNS servers and their caches of the old value expired much sooner.

BT's OWA DNS servers are most probably caching your old MX record value, thus attempting to send to the old location.

Alternatively, do you (or did you) host your domain anywhere near BT's system? If so, they may have an internal MX record for that domain, so they are delivering to that address rather than querying public DNS for your proper, external location.

>> Also how does exchange route replies to emails?

That ultimately depends on BT's set-up. If using Exchange 2007/2010, on a large system such as BT's, they will most probably have different Client Access Servers (CAS) or CAS arrays for each service - POP, IMAP, SMTP via Outlook and indeed, OWA. Again, dependent on topology, each group of CAS boxes may be responsible for routing to the Internet, or outbound Internet mail may go through one set of designated CAS servers.

Outbound email is treated just as if it were a fresh message, so MX records will still be used to route the mail. Message headers have nothing to do with reply email. I cannot suggest why replying to email works but a new message does not; I would simply put that down to the complexity of BT's OWA system and the fact a message could take more than one path through their system to reach you.

-Matt
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tigermattCommented:

>> The email header will have a "reply to" field in it and it is used to route emails back to the sender. So you are right, It uses the Header Info.

To clarify, the Reply-To value in the message header is the SMTP email address the sender requested the message is routed back to. This is normally the same as the sender's address in the From header, but it can be changed reasonably easily in Outlook for outbound email.

The Reply-To value is NOT used to define the actual path the server should use (i.e. the mail server to communicate with) to route messages back to the sender.
0
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BenthamLtdAuthor Commented:
Hi,

I'm thinking this is an issue with BT's OWA.

I can send emails from hotmail and other customers exchange servers into this exchange server fine.
I also use a backup mx service, and when testing the backup, "By stopping the exchange servers smtp" all email from hotmail, excite and other customers exchange servers all queued up at the backup mx providers server.

When I sent in a btconnect.com email from BT's OWA, it didnt appear in the backup mx queue.

So it must be related to BT's OWA.

I will give it some more time.
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tigermattCommented:

>> I can send emails from hotmail and other customers exchange servers into this exchange server fine

That is pretty conclusive.

If the majority of the test cases you used worked, that would tend to imply your configuration is good.

Give it another 24 hours and BT may have flushed their cache.

-Matt
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Hilal1924Commented:
Agree with Matt. Wait for some time and all shall be OK.
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shauncroucherCommented:
Matt has already provided accurate answers to your question, you might also consider finding out what the ttl is for your mx record, this will give a clearer picture as to how long old records should remain alive on caching dns servers.

see my blog entry here which details this;

http://exchangeshell.wordpress.com/2010/03/12/exchange-send-connector-ehlo-and-dns-data-rdns-ptr-mx-spf-txt-a-record

shaun

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