MailHop Backup MX -- Readme

Internet mail is actually a fairly fragile thing, and incorrect MX records up will result in lost messages. When using MailHop Backup MX, you must ensure that mx2.mailhop.org is listed with a lower Preference than the primary mail server for the domain. If mx2.mailhop.org has the highest priority, it will simply reject mail back to sender, as it relies on MX records to determine the destination mail server.

MailHop Backup MX has no limit on the number or volume of messages that it will store for your domain during downtime under normal conditions. (If a problem occurs that causes a large build-up of queued messages, such as tarpitting, we will contact you regarding the problem to help you resolve the issue.) However, MailHop Backup MX has a per-message limitation of 10MB. Messages larger than 10MB will be rejected back to sender with a useful error message.

A common tactic used by spammers is to target the lowest-priority MX record for a domain, and deliver mail directly to the backup server instead of the primary. Because most backup servers have fewer anti-spam measures (to ensure proper storage and redelivery during problems), this can be used to deliver spam that would otherwise be properly scanned and dropped.

To help prevent this tactic from affecting your MailHop Backup MX service, we recommend configuring your domain's MX records in a primary-secondary-primary configuration. By adding your primary mail server as the lowest-priority record, under mx2.mailhop.org, spammers will end up delivering their wares to your primary directly, where it will be dealt with appropriately. Here is an example configuration:

Using this primary-secondary-primary configuration should help reduce any spam you may otherwise see flowing through MailHop Backup MX.

For the first twenty-four hours after the host fails, we will attempt delivery every 15 minutes. For the next four days, we will retry every hour. For the next five days (up to a total of ten days from the original failure of the host) we will retry every 2 hours. Our mail servers will also automatically retry delivery (and re-start this process) upon host status changes (such as a change to your server's IP address).

Attempted deliveries from postmaster@mailhop.org, when originating from mailhop.org-named servers, are just an indication of recipient verification being performed by our servers. Whenever someone attempts to send a message through our servers to your domain, we will first attempt to contact your server(s) and verify the recipient(s) of the message. This way, we can avoid accepting the message if the recipient(s) are not valid. Don't worry, this is not an attempt to break into your system, it is simply an optimization to save server resources for you and us. Don't worry about your server being down, either - if your server is unavailable, we assume all recipients are valid, and sort out the invalid ones once you come back online, so you won't miss any mail!

MailHop Backup MX is not intended for use with third-party mail hosting providers, or spam filtering providers such as Postini. MailHop Backup MX should only be used for primary mail servers which you own and operate. Most mail hosting providers do not offer whitelisting by sending servers, and may block the MailHop Backup MX service for "spamming" as it attempts to redeliver stored mail for your domain.