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Changing external IP address of exchange server

Hello,

We are switching over to a new ISP and have a new static IP for our mail server.

Currently:

A record:
mail.ourdomain. com 1.2.3.4

MX record:
mail.ourdomain.com.(10)

I was wondering if I could do the switchover during the work week by adding a second mx record pointing to the new IP address a day or two ahead of the switchover.

Proposed A records:
mail.ourdomain. com 1.2.3.4
mail1.ourdomain. com 2.3.4.5

Proposed MX records:
mail.ourdomain.com.(10)
mail1.ourdomain.com.(20)

However, on the exchange server, it is setup to respond mail.ourdomain.com in response to HELO or EHLO.

Will this cause problems for sending and/or receiving?

Thanks,
Bonnie

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Jamie McKillop

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Manpreet SIngh Khatra

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Seth Simmons

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Bonnie_K

ASKER

TTl is at 7200, what should I change it to?

Jamie McKillop

Change it to 300

JJ

Bonnie_K

ASKER

OK, I changed it to 3600 yesterday (that's the lowest network solutions would let me change it to)

Then, I added a reverse IP lookup on the new static IP via the ISP - did that this morning.

I used mail1.ourdomain.com for the reverse DNS on the new IP.

My thought is - Wednesday night (36 hours from now) - I will:
1. switch the routers
2. change the HELO reponse on the exchange server to mail1.royalchemical.com
3. swap the MX records, put new static as priority 10, "old" static as priority 20.

Then, we should be able to send/receive email on the new static.

Does that sound like it will work? If not, I should just wait for the weekend.

Thanks very much for the help so far.

Jamie McKillop

You can certainly do it that way, but I think you are making more work for yourself than needed and you could run into problems. Ideally, MX records are supposed to work that the sending server tries the lowest value MX and if there is no response it tries the next lowest value. In reality, it doesn't always work that way. The sending server can end up trying any MX, regardless of weight, and may not fail over to another MX. So, having an invalid MX can cause mail delivery issues.

If you do what I suggest and just change the IP of your current A record, the worst that will happen is that it will take up to an hour for the change to take effect. During that time, the sending server will just keep trying to send. Once the IP updates, it will go through without issue.

JJ