Say you have your own email server stationed at your place of business. And say you have a remote website with a domain name that is set up so that the MX records point to that email server. Then, for whatever reason, your local internet provider changes your email server's IP address, and so there is a few hours where the MX record is not updated on the web server. What happens to the emails that were sent to you in that time period? Are they lost, or will you get them eventually?

No expert, but I used to run my own mail server on a dynamic IP address. I had everything setup as if it was static and my IP rarely changed, but if it did, then anything (web or mail) which was pointed to that IP would not work. Or maybe my server was down for a short period of time.

My experience is that the sending mail server will see that it's can't connect and then will retry. At some point I believe it will stop retrying and usually report back to the sender that it couldn't deliver the mail. I "think" that by default many servers will try for at least 24 hours.

If you are planning on doing something like this in the future, you can have your DNS setup so that your values will live for a very short time in everyones local DNS caches. So this means you can change IP and should have a very short outage. But if your ISP yanks your IP out from under you with no warning, you have to wait for the updated DNS info to filter down to everyone as their local (outdated) copies expire.

If your ISP does not offer static IP, you can use some of the dynamic IP services. I've used no-ip before and it works pretty well.


No-IP

Ive been a member of easydns for three years, I used to use thier dynamic dns stuff, and i will probably continue now that i need to. works flawlessly

if you dont mind something.reactornet.net, i can give you a freebie address.

Assuming that the IP changes are permanent, the MX records need to be changed to point mail to the new IP addresses. DNS changes can take upto 48 hours to propagate throughout the Interweb. So... if you change it now, some mail may be lost, but the senders will get a message saying that the mail was not delivered.

Mostly the DNS changes, at least domestically, happen very quickly and you should be updated in most servers within a day.

Hope that answers your questions.

Any time I take my mail server offline I have my ISP queue the mail. There are also third party services for mail queuing. But if you don't have any offsite queuing in place, messages sent before propagation is complete will be lost / undeliverable.