MailHop Backup MX

This guide will help you set up the MailHop® Backup MX service.

What is MailHop Backup MX?

MailHop Backup MX is a mail redundancy service. If your primary mail server experiences an outage, MailHop Backup MX will receive the mail for your domain and hold it for up to ten days, automatically retrying delivery until your mail server returns to service.

How do I set it up?

Please complete the following steps to get started with the MailHop Backup MX service. This guide assumes that you are using our domain registration and Custom DNS services, though they are not required to use MailHop Backup MX.

1. Create MailHop Backup MX

The first step is to create the MailHop Backup MX service for your domain, e.g. mydomain.com. (Remember, MailHop Backup MX is a domain service, so enter the domain name itself, not the primary mail server.) After purchase, please allow the service at least fifteen minutes to activate.

2. Configure your MX records

To allow MailHop Backup MX to receive mail for your domain, you will need to add mx2.mailhop.org to your domain's MX records. If you are using Custom DNS, you may simply click the Set for MailHop button to automatically add mx2.mailhop.org as your lowest-priority MX record. If you are using third-party DNS or the Expert interface, your MX records should look like this:

Host TTL Type Data
example.com 43200 MX 10 mail.example.com
example.com 43200 MX 20 mx2.mailhop.org

You may include as many other MX records as you like, as long as mx2.mailhop.org is not the highest priority MX record. Please note: If mx2.mailhop.org is listed as the primary MX record for a domain, mail it receives will be rejected to sender (since it can't find a higher-priority mail server to which it can deliver the message).

3. Configure your mail server and network

To ensure you do not lose mail during an outage, you will need to configure your server to accept connections and mail from MailHop Backup MX. The first step is to whitelist our IP addresses to prevent your server from applying anti-spam tactics such as greylisting or tarpitting against us. You can view our full range of IPs here.

If possible, you should add these addresses to the "trusted forwarder" section of your anti-spam service. This will allow your server to properly scan incoming messages for spam without accidentally blacklisting our servers. You will also need to allow these IPs in your firewalls or router if you only allow certain addresses to connect on port 25.

In addition to basic whitelisting, there are a number of potential configuration problems that can occur that may impact our ability to deliver mail to you. Please see our Things Not to Do with MailHop Backup MX article to avoid problems in the future.

Troubleshooting

Mail delivery problems can often be difficult to troubleshoot, as there are many points along the way where a message could be delayed, rejected, or even silently dropped without the sender ever knowing a problem occurred. Please check the following entries and our Things Not to Do with MailHop Backup MX article to see if they describe your problem; if not, you can contact our support team for further help.

When contacting Support, please send the full headers of any delayed or rejected emails (including timestamps and Received: entries) where available, and describe the timeframe of the problem to the nearest hour with timezone. Please make sure you contact Support using an email address outside of the problem domain to make sure we can contact you!

Mail is delayed for hours, then arrives all at once.

This is a symptom of greylisting, where a mail server will temporarily reject mail (4xx error) to deter spammers. You must whitelist our MailHop Backup MX addresses in your server to prevent these delays.

My mail is being rejected with a 550 User Unknown error.

Unless MailHop Backup MX explicitly receives a 5xx Permanent Failure error from your server, we will not reject email with this form of error. Please review your mail logs to determine if your server is misconfigured before contacting Support, and be sure to provide any strange snippets of logs and full headers from the rejected emails.

There are many potential causes of this problem, but here are some of the most common:

My mail server is down. How often do you try to redeliver my mail?

For the first 24 hours after a failure is detected, we try to redeliver your mail every 15 minutes. For the next four days, we retry delivery every hour. For the remaining five days, we retry every two hours. After ten days, stored mail is bounced back to sender.

I receive a lot of mail. What are the queue size and message size limits?

MailHop Backup MX does not limit the total volume of individual messages it can store or redeliver. The service has a per-message size limit of 10MB; individual messages larger than 10MB will be returned to sender with a useful error message.

I'm getting spam for mailboxes that don't exist.

Your server does not have recipient filtering enabled. Recipient filtering checks to make sure a receiving address exists before accepting the content of a message, returning a 550 User Unknown error to the sender for nonexistent mailboxes. Without recipient filtering, your server will accept any email, then later send a non-delivery report (NDR) back to the origin (a waste of time with spam).

As mentioned above, MailHop Backup MX uses call-aheads to verify that a mailbox exists before accepting and redelivering the message to you. By enabling recipient filtering, you reduce the load on both your server and ours as we block nondeliverable mail right at the start. Exchange users can learn how to enable recipient filtering here. Customers can also use the User List in MailHop Backup MX to block invalid recipients at the service level.

I'm getting a lot of spam. Can I block more of it with MailHop Backup MX?

MailHop Backup MX does not perform any spam scanning or virus elimination. You can enable additional DNSBLs to block spam from known bad senders, or you can use MailHop Relay instead (which features a variety of anti-spam options).

You can also change your MX records to a primary-secondary-primary configuration. Many spammers automatically target the lowest-priority MX record by default to bypass the anti-spam filters on the primary mail server. To help prevent this, adding the primary MX again as your lowest-priority record will thwart this tactic:

HostTTLTypeData
domain.com43200MX10 mail.domain.com
domain.com43200MX20 mx2.mailhop.org
domain.com43200MX30 mail.domain.com

I want to use an anti-spam service like Postini as well as Backup MX.

Unfortunately, you cannot use MailHop Backup MX and a third-party anti-spam service simultaneously. You can learn more about this here.