Beating Spam and Viruses with amavisd-new and Maia Mailguard
Maia's Web-based interface lets users authenticate against a variety of sources, including a POP3 or IMAP server, an LDAP server, an external SQL database or Maia's own internal database. Users can be added manually by an administrator or automatically when mail arrives for a local address that Maia hasn't seen before.
Users can have multiple e-mail addresses linked to their accounts, but each e-mail address has its own content-filtering settings (Figure 1). Users can add and remove addresses from their whitelists and blacklists with the Web interface (Figure 2), while administrators manage domain-level and system-wide settings from another set of Web pages (Figure 3). Statistics are maintained for all four of amavisd-new's mail types, as well as blacklisted and whitelisted items, oversized items, false positives and false negatives (Figure 4). Other tables keep track of viruses by type and by how often specific SpamAssassin rules are triggered. Graphical charts can be generated on the fly from this data or generated as static pages at scheduled intervals.
Thanks to the fact that Maia puts quarantine management and content-filtering controls in the hands of users themselves, there isn't a lot of work left for administrators to do on a day-to-day basis. With Maia's Perl scripts running at scheduled intervals to report user-confirmed spam and to expire old quarantine items, the system all but manages itself.
When mail gets quarantined on behalf of a user, it's important that the user has a convenient way to access that mail. Maia provides a list of the items in a user's quarantine, sorted by spam score so that the items most likely to be there by mistake—the false positives—are kept closer to the top of the list and are easier to spot (Figure 5).
If you're not sure from the subject line whether the mail is legitimate, you can click on the subject to open the e-mail in Maia's mail viewer (Figure 6). The mail viewer is safe to use on all types of mail, as it doesn't decode most attachments but does block remote images and strip away HTML tags that could redirect you to another site. You can view the mail in its decoded form or in its raw form, complete with all of the original mail headers.
If you decide that the mail is legitimate after all, you can click a button to rescue the item from your quarantine and have it delivered to you. At the same time, Maia tells SpamAssassin about the mistake; the Bayesian learning system is less likely to make the same mistake in the future. You also can configure Maia to add the sender's address to your whitelist automatically when you rescue an item in this manner.
In addition to the quarantine, Maia offers a ham cache, which essentially is a list of the legitimate mail that you've received recently (Figure 7). The purpose of the ham cache is to let you report spam that somehow got past the filters—the false negatives. By marking these items properly as spam, you help to train SpamAssassin's Bayesian learning system.
The quarantine and ham cache also provide a means for you to confirm the status of the mail you've received. This not only helps train the Bayesian learning system, it also makes it possible to report spam properly, because it's been confirmed by a human being.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide