Backup MX Server - SmarterTools

We are currently running SmarterMail to host several domains. I would like to switch over and use SmarterMail as the backup MX server as well. I can follow the kb article for doing so, but my question is how can I prevent the backup MX server from accepting and queuing email for domains that are not currently hosting on our primary SmarterMail server? For instance we accept domain1.com, domain2.com, etc. I'm not seeing from the kb where I can prevent it from accepting email at domain3.com. Probably overlooking something... Thanks in advance,

On the backup server, go to routing and incoming gateways. Set gateway mode to backup mx, give it the IP of your primary server you want it to be back for, set user verification to web service and then check the box to enable smartermail gateway mode. This will log into your main server and verify the mailbox first. Robbie Wright February 19, 2016 at 10:19 AM

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The server it's forwarding too is not necessarily a SmarterMail server though. I'm almost thinking it should be a domain forward and then a list of domains afterward. If we do domain forwarding, should I have a separate line for each domain? If not is there a limit to the number of domains per each record?

What is the main difference between a domain forward record and an MX backup record? they seem to do the same type of thing through testing. Anthony DePinto February 19, 2016 at 10:48 AM

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Domain forwarding will actually process the mail for you. Backup MX should, depending on how it is configured, just hold the mail until the main server comes back online. I'm not aware of a way to have SM only provide backup services for specific domains without using their API in an existing SM server to verify if the domain is hosted there. Robbie Wright February 19, 2016 at 11:26 AM

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Hi Anthony. I wanted to chime in because I just set up Domain Forwarding in Smartermail for one of our customers this morning. Domain Forwarding and Backup MX are two different things. For example... If you have a primary server and you want to use the Smartermail server as an antispam gateway for the primary server, you can set up Domain Forwarding in Smartermail for your primary mail server. What you would do is add an Incoming Gateway. For the Gateway Mode option, you would choose Domain Forward. Then you would add the IP of your primary server. You can put a check in Disable Graylisting if you like. If your primary server is also a Smartermail server, you would need to put a check in the "Enable Smartermail Gateway Mode" box and choose whether or not you want to use User Verification. If you do, pop down the User Verification box and choose "Web Service". Once you do that, click the Smartermail Gateway tab and enter your URL and admin information for your Smartermail Admin interface. Next, click the Domains tab and enter the domain names that you want the server to accept mail for. Whatever domains you specify, be sure to point the MX records to the Smartermail server so all mail for those domains will be sent to it for spam scanning. Once Smartermail scans it, it will be delivered to whatever recipients it was addressed to. If your primary server is not a Smartermail server, you can skip the steps that I mentioned about in reference to Smartermail Gateway mode.

So to summarize, Domain Forwarding is used when you want to use the Smartermail server as an anti-spam gateway for your primary server.

Now, Backup MX is different. This is used as a Store and Forward type feature for your primary mail server in case it ever goes down. If it goes down, mail will be sent to your Smartermail server and held there until your primary server becomes available again. As far as I know, you cannot set this up for a per-domain configuration within Smartermail. However, there is a work-around. If you set up Backup MX and your primary server goes down, all mail sent to the primary server will instead be redirected to the Smartermail server and held there until your primary server is back up. In order to make this work, you would have to add secondary MX records to your zones in your DNS for mail which point to the Smartermail server. So basically, when someone sends mail to someone on your primary server, and it's down, it will send to the secondary MX, which is your Smartermail server and the Smartemail server will hold the mail.

Now, about the workaround... If you wanted to set up a Backup MX, but you didn't want it to catch mail from certain domains if your primary server goes down, all you need to do is NOT add the secondary MX record to your DNS zones for those domains. I'm not sure why you would want to omit domains from the BackupMX, but if you do, that is how you would do it. Just be aware that if you omit domains from the Backup MX and your primary server goes down, all mail to those particular domains will be bounced back to the senders.

I hope this helps. Take care! Linda Pagillo February 19, 2016 at 11:53 AM

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I suppose I could try this out, but if somebody already knows the answer... If I setup SmarterMail with the backup MX record and I create secondary MX records for domain1.com and domain2.com, I understand it will accept email for those and relay on or queue if the primary mail server is down. Who's to say somebody wouldn't send email for domain3.com (a domain we don't host) directly to this backup server and use it as a relay agent? Will Smartermail look to see if there is an MX record pointing to it in order to accept the mail or will it relay/accept mail for any domain that hits it? Anthony DePinto February 19, 2016 at 12:56 PM

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Smartermail will not accept mail for a domain that it's not configured to accept mail for. However... spammers will spam the secondary MX records directly. There is nothing you can do to prevent them from doing this, so it's very important to have good anti-spam software that will filter the junk that is hitting the secondary MX. Linda Pagillo February 19, 2016 at 1:41 PM

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understood, but if I'm just adding the backup mx record where it should point mail to, I'm not really defining a list of domains anywhere. how will smartermail know to not accept and queue a domain that we don't host? that's why I was wondering if it looked at MX records when a message came in to determine if it "should" allow it. Anthony DePinto February 19, 2016 at 2:18 PM

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Do all of your mail domains share the same MX record? If not, what leads you to believe that any messages would be sent to the Smartermail server to hold if they are not for your domains? Linda Pagillo February 19, 2016 at 3:15 PM

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