add a backup smtp server

You mean to say that if your sbs server dies then you need to pint your mails to some where elese is that right. if so then below link explains the procedure about how to do that.
http://www.amset.info/exchange/smtp-backup.asp

This document relates to Exchange being used as a backup server.

I need the web host to be the backup server and exchange to be the main (first) server.

I don't think you can have a web host as  backup server.only thing is point you mx records to your web host.

You could simply add an MX record pointing to your web host's mail server, with a higher cost than the one going to your server. However, that's a bad idea, because you're going to have to create mailboxes at your web host for every address on your exchange server, or use a catch-all account which means a lot of administration afterwards.

Instead, you should really be looking at why you need to have it going to the web host instead, and why you think your server might go down. If it's really critical that you have a backup then I would get a second exchange server, (I think you'd need to migrate to a 2003 Standard domain first though) install it into the existing organization then you won't get the problems you've got with if you used the web host.

Also, don't forget that any well-configured mail server will try for up to 48 hours to keep sending the message, so if the server is only down for a few hours it shouldn't be a problem.

This is what Ive received by the web host.

I dontknow what do with this.

You do not want to add the Exchange server to your MX records, because then some mails will be delivered to your web host, and some to your Exchange server. What you would want to do is to create a hostname like smtp.yourdomain.com, and configure it to do load balancing between your Exchange and webhost server (e.g. http://content.websitegear.com/article/load_balance_dns.htm), then configure your users' email software to use smtp.yourdomain.com instead of mail.yourdomain.com and you would need to make sure that your users with mail normally hosted on the webhost will be able to authenticate and send mail properly from the Exchange server. We would not be able to support you in configuring Exchange or your DNS settings.

Load balancing between the web host and Exchange is a bad idea, since they are two separate systems, so you'd have to maintain two separate sets of mailboxes, email addresses etc. Think about the administration nightmare!

From what they've said "You do not want to add the Exchange server to your MX records" it sounds like you don't already have Exchange on the MX?

In my above post I did state that most mail servers will retry for anything up to 48 hours, so unless you expect your server to be down longer than that it shouldn't be a problem.

There are onyl 3 mailboxes on the domain. SO I will have to deal with the administration side of things.

SO how do I do this?

When you say cost you mean order. Is this correct.

Example.
Ns1= exchangeserver ip
ns2 = webhostip.

Problem is, at the moment I have two ns records for the domain.
So do I have to setup up a ns record for smtp.mydomain.com and then put this as ns3. And do I do this via my domain registrar.

For example
Ns1= exchangeserver (ip)
ns2 = webhost (ip)
Ns3 = smtp.mydomain.com (ip)

Apologies for not getting back to you on this one. If you follow the above information, that should get you up and running.

tigermatt

I dont quite know where to put this information.