MegaMail

By front-ending a coordinated, load-balanced mail server cluster, Bluetail Mail Robustifier virtually eliminates email reliability and scalability worries. It's green, but we think the benefits make it worth any ISP's while to take a look.

by Lisa Phifer VP Core Competence, Inc. [May 4, 2000]

ISPs and their customers may not always see eye to eye, but on this point they agree: Email is a mission critical app. Woe be the ISP who takes mail server reliability lightly. Successful ISPs know that losing a mail server means losing customers. Most stand ready with a replacement server to limit downtime in the event of mail system failure. Bluetail Mail Robustifier goes one better: it allows a physical server cluster to work together as one robust, high-availability virtual mail server, insulating the ISP from single-server failure.

High-Availability and Scalability by Proxy
Bluetail Mail Robustifier is a POP3, IMAP4, and SMTP proxy, designed for deployment as a high-availability front-end to back-end mail servers. Although Bluetail will operate on a single machine for evaluation purposes, it is really intended for medium to high volume mail sites with at least two physical mail servers and one front-end proxy. A high volume site may have dozens of back-end mail servers, organized into clusters, with redundant NIC connectivity to several front-end proxies.

To understand how Bluetail Mail Robustifier works, consider this example configuration: a pair of front-end systems proxy mail on behalf of four back-end mail servers. Only the proxies are externally visible (i.e., associated with MX records). These proxies are configured into two clusters: an SMTP cluster with proxy "A" as primary, and a POP cluster with proxy "B" as primary. The four back-end servers participate in both clusters, allowing workload to be distributed across servers according to configured thresholds.

If one proxy should fail or be taken out of service, the other will take over transparently, covering both SMTP and POP. Similarly, back-ends can be added or removed transparently, with proxies directing traffic to avoid server overload. This type of configuration offers redundancy and scalability when compared to stand-alone mail servers, and can be used with a combination of mail servers (e.g., sendmail on back-end "X", qmail on back-end "Y").

Load Balancing and Mail Session Routing
Bluetail provides built-in failure handling: if one proxy goes off-line, another takes over its IP address. In our example, proxy "B" might be mail.ourdomain.net, with proxy "A" assuming this address when proxy "B" goes down. Arriving traffic can also be distributed across several active proxies by round-robin DNS or using a layer 4 switch.

If back-end mail servers share a common (e.g., NFS) message store, Bluetail balances load across all servers based on configured parameters like response time, run queue length, mail queue length, and disk utilization. If back-end mail servers use separate message stores, mail sessions must be routed to the server or servers who own a given mailbox. Mail sessions can be routed by user or domain, driven by mapping tables supplied in text format or drawn from an external (LDAP, SQL, or RADIUS) server database.

If a back-end server goes off-line, proxies automatically re-route requests to other servers—or reject requests if no suitable server is available. In fact, if Bluetail detects that a server is becoming overloaded (e.g., queue length or disk utilization at defined threshold), it re-routes or rejects traffic to avoid a server crash. This Mail Robustifier feature helps the cluster survive sudden bursts of legitimate or spam traffic that might overwhelm a stand-alone mail server. Different thresholds can be defined for groups of users, so that premium users can receive priority when regular users are being deflected during periods of heavy traffic.

Custom Handling for Troublesome Domains & Users
As an SMTP MTA, Bluetail Mail Robustifier supports standard anti-spam measures. It can accept or reject SMTP connections based on domain name or IP address, block incoming mail from specified domains, and block outgoing mail sent by or to specific users and domains. Custom handlers can be written using Mail Robustifier's "hook" interface. For example, Bluetail has used this interface to build a pop-before-smtp utility that implements POP3 session authentication for SMTP relaying (available at no cost from the Bluetail website).

With Bluetail, administrators can also configure separate SMTP mail queues for selected domains. When doing so, any mail previously queued to the affected domain is automatically moved to the newly-created queue, unclogging the existing queue so that others aren't affected by the troublesome domain.

Bluetail Installation and Management
Bluetail Mail Robustifier proxy software runs on Sun Solaris 2.6/2.7, Linux 2.2+, FreeBSD 3.x, BSDI 4.0, and Windows 2000. It can be used with any SMTP/POP/IMAP server running any operating system, although load balancing metrics are limited on Windows platforms.

All Mail Robustifier proxies run under the supervision of a management server—the Bluetail Cluster Manager—installed on one of the proxy systems. The management server provides both command line and Java-based graphical interfaces for single-point configuration and monitoring. Configuration changes and even software updates can be completed without shutting down the mail system. Changes are entered at the management server and then internally propagated to cluster members—even those that happen to be down at the time the change is made.

All proxies record statistics, events, and alarms in a local log. Local logs merged and stored by the management server, providing a consolidated record and view of mail system behavior. The newest version, Bluetail, Mail Robustifier 2.1, also supports SNMP traps for admin notification of exceptional events and audit trail logging to track configuration changes.

Pricing and Support
Interested in trying Bluetail Mail Robustifier? A 30-day trial can be downloaded from the Bluetail website. Once you're hooked, you can either lease or purchase a permanent license. Bluetail Mail Robustifier for up to 15,000 mailboxes can be leased for $450/month or purchased for $9,000. Bluetail will quote "stair step" prices for larger installations based on number of active mailboxes; contact info@bluetail.com. Support contracts are available for 20 percent of the purchase price.

Bottom Line
Bluetail is a relatively new company, formed in 1999 by a crack team that hails from Ericsson. Bluetail Mail Robustifier is therefore a fairly young product in an arena that, by its very nature, demands maturity. The product sounds quite promising: high-availability, robust, reliable mail server clusters with the ability to support classes of services through prioritized handling. But the proof of the pudding is in the eating. To this end, we look forward to seeing Bluetail publish customer success stories as this product proves itself in the field. ISPs seeking a way to improve mail server scalability and reliability may be wise to take a closer look at this product.

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