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Breaking up is hard to do

Posted on 3 Mar 2009 at 17:05

Mark Newton discusses how best to part ways with your current ISP and move to a new one, and finds out more about the Azure cloud.

If you can't re-configure things at your old ISP to redirect web traffic to your new web server, the next best way to achieve almost the same result is to remove all the files from the old web server and then put your redirection code into the 404 error-handler page (the page that's served when a requested page isn't found on the server). By making such changes to your old web server you can be sure that should the DNS changes take a long time to propagate around the internet, visitors to your old website will arrive at the correct new one.

A example of adding redirect code to a static HTML page might be like this:

Please wait while we redirect you to our new website

So with your new website up and running on your new server and visitors being redirected, you can now make the changes to your DNS to point the "WWW" hosts file entry to the new server's IP address. The changes should be seen within 24 to 72 hours, but expect at least another two weeks for the changes to be fully propagated around the internet and all the old IP addresses to be flushed from various DNS and proxy servers out there. (For some reason, AOL users always seem to be among the last to see such changes.) Once everything has settled down, you can finally stop using your old ISP for web hosting.

Now let's consider moving your email hosting to a different ISP, which can also cause a few problems. The first question to ask your new ISP is whether it supports "authenticated SMTP", which enables you to send email from any network, or whether you can only send emails if your mail server is on its network. There are two main types of mail hosting: one in which your emails are held on the ISP's server and you log in to collect them either via a web interface or a mail client such as Outlook; in the other scenario, you run your own email server and your ISP sets the DNS to point its MX record to the external IP address of your mail server. Let's assume that you're not moving your ADSL supplier at the same time, because if this were the case your external IP address would be changing too, and you'll have other problems. Save that for another day and don't try to move it at the same time, otherwise it could all end in tears.

Taking the scenario where you're running your own email server first, you'll need to tell the ISP that's going to be handling your DNS where to point the MX record of your domain, and you also need to be sure that the external SMTP address on your email server is pointing to the correct ISP's mail server. Bear in mind that a lot of ISPs won't allow you to send emails through their SMTP servers if you're not part of their network, so if your ADSL is supplied by another ISP you'll need to use that ISP's SMTP server address for outgoing mail, configured either in your mail client if it's holding your emails, or in the configuration of your own email server. In the other scenario, where the ISP holds your mail on its servers and you collect it, then as soon as you point your DNS at the new ISP your email will start to go to its server - before you move to the new service, you'll just need to do a final login to your old ISP and download any email not yet gathered from there.

ISPs usually run POP mail servers, which means that when you log in to get your email, once it's downloaded to your client or server it will be deleted from their mail server, so be aware of this and plan your steps accordingly. Once you're sure you've got all the emails you want, you can cancel the mail service on your old ISP and then enable the DNS changes for the new ISP. Any email arriving while this changeover is taking place should fail to find a mail server, then "bounce" and be automatically resubmitted (usually for up-to five days). Once again, it's very handy to have the full co-operation of your old ISP during this process. If your email client uses the full names of the servers and not just IP addresses then, assuming the new DNS has entries for those names, you shouldn't have to change anything at all in your client.