Create a Backup Mail Server for Exchange

In our test lab we have one Exchange Server 2003, (Exchange1), behind a firewall which works fine.

However I want another server to accept incoming mail so if our exchange box goes down it will still collect the incoming e-mail and hold it until the exchange e-mail box comes back on line then passes it to the Exchange Box, (Exchange1), which in turn delivers it to the correct mail box.  

I know I need to create another MX record with a higher cost but what do I need to achieve my result ?  Do I need just another exchange box, or can I use SMTP and IIS on a 2003 server ? Pointers and advice would be very much appeciated.  
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You can use a plain Windows 2003 IIS machine. However if you use a standard IIS server you would lose recipient filtering. You would also have to ensure that the server is protected with the same level of AV and antispam protection as your primary server.

The major problem with second MX records is that they are a spam magnet.
Instead, what I tend to suggest is a second MX record using a Dynamic DNS account.

The key thing is what you are planning for. An Exchange server correctly built will not go down very often, if at all. An email server being down for a few hours is something that most companies can tolerate and will not result in loss of email.
If you are going to be down for more than 48 hours (the usual timeout for sending servers) then you will have bigger things to worry about.


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And if you decide that you don't want to set up another box you are more than able to call your ISP up and have them activate their fallback so that they will be the secondary MX record and will store emails for you should your server be down. They will give you a far longer timeout than the default, should you so require it.
After all, a link is just as likely to go down as a server.
tickleonthetumAuthor Commented:
Thanks for these guys.  Its a lab enviroment and I'm trying to understand how you would setup the backup server if required.  So, Simon, lets assume for what ever reason the exchange box is down and will be down for some time.  I want the mail to be delivered automatically to another mail server can I do this with IIS and SMTP on a Windows 2003 server, (Enterprise Edition).  If so can you point me in the direction of an article or advice on how I setup the IIS and SMTP to achieve the result I want ? i.e receive the mail, (that bits easy), but forward it automatically to the live exchange server when it comes back on line ?
czcdctCommented:,295582,sid14_gci1094072,00.html?track=websecland is the nice article. It tells you how you will set up the SMTP server. The MX records in the global DNS is a matter of conversation between you and your ISP. If you have more than one fixed IP address you're in business. You do the translation on your firewall/router to send mail as a primary to the Exchange and as a secondary to this IIS box. It does not need to be in the DMZ should you so choose.
Your DNS records will have two MX records pointing preference 10 to "" and a secondary at preference 20 pointing to (whatever). There will obviously be A records for mail and holding. A sending server will automatically look up the MX records, be given the answer and try to deliver down the list.
Make sure you hold the mail on your IIS for as long as you ever think you're going to be down by.

As a general rule I would suggest the ISP fallback route first since it's cheap and involves no infrastructure changes. If you are absolutely sure that your link(s) to the Internet are solid and secure then the IIS route is the way to go.
tickleonthetumAuthor Commented:
Thanks Guys.
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