Merce MailGate protects against spams and malware by deploying various different layers of security.

• Virus filtering. Merce MailGate filters all emails for viruses. This filter filters each file inside zipped attachments if the zipfile is not password-protected. It searches all types of files, including Web pages attached to emails, scripts, macros, etc, to ensure effective filtering.
• Spam filtering: sender checks. Merce MailGate checks the sender address for authenticity, and demands some degree of credibility for the originating IP address, before it allows emails to enter. It has the power to distinguish between statically and dynamically allocated remote IP addresses, and can block all mails from dynamically allocated IP addresses. It also uses various key black-lists on the Internet and blocks known offenders.
• Spam filtering: connection credibility checks. Merce MailGate observes the protocol compliance of the remote SMTP connection and notes other differences between the behaviour of typical primitive engines used for spam transmission and legitimate email servers. When it detects these signs of non-standard behaviour, it blocks emails from those sources.
• Spam filtering: attachment policy enforcement. Merce MailGate permits a customer to enforce policies about the sizes and types of attachments that it wishes to permit over email. This is used to block transmission of executable binaries over email, or carry large multimedia files in a corporate business environment which does not expect such payload. This reduces the likelihood of malware entering the enterprise email network, because attachments often contain malware designed to exploit specific types of vulnerabilities in desktops.
• Spam filtering: Bayesian content filters. Merce MailGate inspects the content of each email and applies a few hundred complex rules about the content and format to arrive at a weighted score of the likelihood of the email being spam. All emails above a cutoff score are rejected. This content filtering layer is fed with samples of malware and genuine emails to help it learn and fine-tune its filtering for each customer.
• DoS attacks. Merce MailGate blocks denial of service attacks by blocking excessive email traffic from a single IP address using automatic rate throttling algorithms. It also integrates with Merce to block dictionary attacks.

If Merce MailGate protects an enterprise network running Merce, then powerful synergy is available for more effective protection, reporting, etc.

• Dictionary attacks. Merce MailGate blocks incoming mails for non-existent recipients by synchronising its list of valid addresses with Merce. Therefore, MailGate knows which recipients are valid, and rejects the rest in real time. This also prevents choking or overloading of the MailGate system with spurious messages which would have been bounced if they were allowed to pass the MailGate.
• Integrated reporting. Merce MailGate reports its status reports and filtering statistics to the central Merce server, thus allowing an integration of the reports and an extension of Merce's class-leading single-window management and reporting interface.
• Intelligent white-listing. Merce reports to Merce MailGate the list of external email addresses which are in regular correspondence with internal users. These addresses are automatically treated as more trusted by Merce MailGate, and this enhances its ability to allow incoming mail from trusted counterparties while blocking spams from unknown sources.
• Merce SourceGuard. Merce MailGate tracks those external email addresses which are in regular correspondence with internal users. If an external sender has never been in prior correspondence with any internal user, then mail from this sender is delivered to the internal recipient's mailbox in a separate folder instead of his Inbox, with higher suspicion rating. This feature, called Merce SourceGuard, is proprietary to Merce MailGate and delivers almost theoretically maximal levels of cleanness for messages delivered to the primary Inbox of each user, while delivering suspicious messages in separate folders.
• Feedback to learning filters. Merce users store their messages in IMAP folders and may use automatic client-level tools or manual sorting to keep aside spams in a separate "Junkmail" or similar folder. Each user's "Junkmail" IMAP folder is then picked by Merce and its contents are fed back to Merce MailGate for training and improving its filtration. This feedback mechanism is automatic, and the only participation needed from the user is to keep his identified junk mails in a separate "Junkmail" folder. Thus, the few spams that a Merce MailGate may miss initially will be fed back to improve its filtration with time.
• Integration with Merce Firewall. Merce MailGate can be installed on the same server which is running Merce Firewall, and the enhanced security of the Firewall, plus the optimisation of hardware resources, can benefit the customer.

Merce MailGate has many features which deliver high performance, and a proven track record of scalability and stability.

• Very high performance. Merce MailGate running on an entry-level single-CPU-socket server with 2GB RAM is able to deliver filtration for 100,000+ message delivery attempts per day with almost zero CPU utilisation.
• Very efficient bandwidth usage. Merce MailGate is designed to apply multiple source reputation and integrity checks at the early stages of the message reception, before the body of the message has been accepted. This typically allows more than 90% of all spams to be rejected before the message body is received, thus conserving bandwidth sharply compared to content-inspection based filtering systems.
• Stability. Merce MailGate does not require operational maintenance, and can run for more than a year without human intervention for any maintenance tasks. There is no leakage of RAM or disk usage with non-stop usage. Zero-downtime installations are the norm.
• Security. Merce MailGate is administered through the main Merce management interface, therefore does not require any local users or passwords to be created or maintained. This enhances security and eliminates the likelihood of accidental leakage of administrative access to the gateway. All administrative traffic is exchanged with the Merce Master Server through key-based cryptographically secure channels.
• Redundancy and high availability. Merce MailGate clusters can be set up to run in parallel and provide high availability for incoming mail flow.