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MX / Mail Setup

goraek used Ask the Experts™

I think we need MX setup correctly as emails dont flow to the exchange server after a day down time.

Our link was down for a day, and after it came back up, the emails dont seem to be coming in. I am beginning to think that we need some sort of a incoming MX queue setup or some sort.

Our exchange knowledge is average, however we need some experts to guide us with this.

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You wouldn't have received any mail if you didn't have an MX record for your domain. Please run the following to lookup your current DNS MX. Replace yourdomain.com with whatever comes after @ in your email addresses. Replace xxx.xxx.xxx.xxx with the IP address of an external DNS server.

At a command prompt:
Type 'nslookup' press enter
Type 'server xxx.xxx.xxx.xxx' press enter
Type 'set type=MX' press enter
Type 'yourdomain.com' press enter
What you need is for a second mail server to receive mail if you have a problem. You would then create a second MX record pointing at this server, but with a lower preference so mail only goes there if your primary is unavailable, i.e.

yourdomain.com     IN     MX     10 mail1.yourdomain.com
yourdomain.com     IN     MX     20 mail2.yourdomain.com

Or ask your ISP to queue your mail for you in the event of an outage


How do I setup to queue my mail internal with MX record?


Also I did a nslookup mx command, it came out with DNS timedout

DNS request timed out.
    timeout was 2 seconds.
DNS request timed out.
    timeout was 2 seconds.
*** Request to cpe-60-230-115-8.lns9.win.bigpond.net.au timed-out
MX is just a method for the sending mail server to find out where to send mail, it doesn't provide any queue functionality. You need to have somewhere for that mail to queue.

What is the domain where mail is failing to arrive?


Ok cool - does that mean it will queue if its directing to the mail server or the external IP of the mail server?
The MX record directs to a DNS A record, so something like mail.yourdomain.com. The sending mail server then looks up the DNS A record for mail.yourdomain.com and that needs to be the external IP of the mail server (or more securely the external IP of the gateway/router that NATs to the mail server).

In the simplest situaton the sender mail server then connects to that IP address and tries to send the mail. If your exchange server is down then it cannot connect and the mail is queued on the sender mail server according to their rules. Normally the sender will retry your server at various intervals before giving up.

To ensure you don't actually miss any mail you need to be able to receive the mail somewhere, even if it isn't on your exchange server. You can do this by making your MX point to something that is always available, such as load-balanced gateways, which receive the mail and then sends it to your exchange server. If exchange isn't available the mail sits on the gateways until it is. Alternatively you give sending mail servers multiple options of where to send the mail, if one fails then they try the other one. This is achieved by multiple MX records as above.
Also, with regards to the fact that your inbound mail doesn't appear to be working, have you checked that the SMTP virtual server is definitely running on your Exchange box and also checked the Event Log to see if it's an exchange rather than a DNS/MX issue?

If you let me know the domain where the mail is failing to arrive then I can simulate an inbound message and let you know if there is something obvious.


Thanks for the extra info.
My in bound emails started to work after I changed my IP. It got changed because my IP is dynamic.