Is it possible to use one domain on two different mail servers?

anyone? please help. thank you.

If I change the mx record, the pop3 email of the ISP won't be affected?  For I still have to keep  it  running as a backup for the exchange. Is sending and receiving from the exchange outside, from exchange to ISP and ISP to exchange will be ok eventhough the other email account is setup exchange and not on the ISP mail?

How can I transmit all the mails from exchange to the ISP?

I think I might have misunderstood your question. Are you intending on creating mailboxes with identical email addresses in both Exchange and the ISP, in order to have some form of backup, or do you want to use Exchange mailboxes for some email addresses and ISP for the other mailboxes?

tigermatt

Yes I want to use exchange mailboxes for other user who doesn't have email addresses and at the same time I will create identical email addresses in both exchange and ISP. After the creation of mailboxes in exchange, if sending and receiving is already ok with some email addresses in exchange I will shift all the mails from ISP to exchange and make the ISP mail as a backup only. I need to have both exchange and POP3 mail running in same domain. Do you think this is possible?

It is definitely possible to configure the ISP as a backup - you can simply set their MX record with a higher cost value (therefore lower preference) to the Exchange server MX record. If the Exchange server is unavailable for any reason, any servers sending mail to your domain would then look to the next available MX record, the ISP's, and transmit the mail to their server instead.

I think to get your temporary split configuration between the ISP and Exchange is going to have to be set up to pass through Exchange. You'll need to change your MX record so your mail is passing first through your Exchange server. As I described in my above post you then need to tell Exchange not to be responsible for the entire domain and to pass mail with unresolved host to the ISP's mail server. By configuring this, all mail sent to your domain will pass through the Exchange server, but if the address doesn't exist at Exchange, rather than generate an NDR, it will instead transmit the message to the ISP's mail server.

I try to uncheck the box and it doesn't allow me to uncheck it, it says that exchange should have at least one primary.

That's because the address you're trying to make Exchange share is currently the primary address. You'll need to create another SMTP address in that policy and set it as the primary (@domain.local or something) - you will then be able to uncheck the box on the domain you are sharing.

http://www.msexchange.org/tutorials/Exchange-2003-SMTP-Namespace-Sharing.html

Sorry I have checked the .local.company.com as primary and unchecked the company.com. One more question though, is your suggestion will work if there is a mail relay?

e.g

exchange 2003 uses smtp connector to forward all mails in the smtp virtual server in the DMZ which has the IIS plus smtp. Will forwarding with unknown recepient in the option of smtp virtual server in exchange will work?

To be quite honest I think the only way you are going to know for sure will be to try it and see what happens as without knowing the exact environment and configuration I can't say for sure.

Ok, thanks for your help.