SBS 2003 - moving from POP3 connector to SMTP - advice needed

[feenster99]

Hi all,
I am setting up a new server at work running SBS 2003 R2. We currently run SBS 2003, but collect email via the POP3 connector. I want to alter this on the new server to use SMTP for the obvious benefits it brings.

However, I want to ensure as little downtime as possible when making the switch, and want to ensure that email can still be delivered if the server is down.

So, on that note, I know I have to change the MX record on our domain. Can I do this in such a way that if the Exchange server is down for a period of time, email is delivered to another source (say the Linux web server our site runs from?). If so, what should my MX records look like? What other best practices should I be aware of to ensure as little disruption as possible?

Cheers,
Matt

 

[PCZ]

Short answer create a second MX record.

When you create an MX record you specify 2 things the name of the mail host and the priority.

Make sure both of your mail servers have names in DNS.
MX records should not point to IP's.

For the Primary mail server give it a priority of 10.
For the Secondary mail server use a priority of 20.

Usually a Primary or single mail host has a priority of 10, seems to be the default.

 

[feenster99]

Hi PCZ,
I understand the principle of MX records. However, my domain currently has two listed, like this:

Type    Record                 IP
A         mail.domain.com    123.123.123.123
A         mail.domain.com    123.123.123.456

Type    Record                 Priority
MX       mail.domain.com    10
MX       mail.domain.com    20

So if i just add in another A record with the new IP address, then add another MX record, there will 3 of each. How does it know which one to use as the priority?

Matt

 

[oddjob62]

Remember to make sure your recipient policy is set to accept the required emails. With the SBS POP3 connector you can forward collected emails to any AD user without the recipient email being correctly set. When you change this to SMTP, if for example an email is sent to [email protected] and that email does not exist on the server, an NDR will be returned to the sender.

 

[Corasik]

Make sure your secondary MX is configured to know your valid email addresses, spammers often target secondary MX's as an easy back door into your mail system, and if your secondary mx doesnt know the valid email addresses, it will accept everything, your primary MX will then reject it, and the poor secondary will probably try to email bounce messages for every error.

 

[PCZ]

Matt

In the Snippet of DNS config you posted above both your mail servers appear to be called mail1.

If indeed this is the case then that won't work as you intend.
They need to have different names if you wan't one to be a backup.

Call the backup mail2

If you don't both your primary and backup records will resolve to the same hostname.
Since the hostname has already been resolved by the Mail server forwarding to you it might not do another DNS query before trying the backup and will send to the same IP.
Even if it does another DNS query chances are it will not be to your authorative DNS but to its local DNS which will have cached the hostname.

If it is your intention to load balance using DNS then multiple IP's for the same hostname such as you have will do round robin.
However if one of your servers goes down half of your incoming mail will be delivered very late or not at all because 50% of the DNS queries for your mail server will be resolved to the IP of the Server which is down.

If you wan't a primary and a backup not a load balanced pair use different hostnames and IP's with different priorities.

A mail1.blah.com 100.100.100.1
A mail2.blah.com 100.100.100.2

MX mail1.blah.com 10
MX mail2.blah.com 20

 

[feenster99]

PCZ,
Thanks for that - I suspected the A records should be different, otherwise it wouldn't know which one to dish the mail out to. Ill re-read the info you've given me tomorrow (when i'm a bit more awake!), and will come back with any questions

Cheers,
Matt