SPAM mails are nuisances! An important customer mail or a pal’s wedding invite may get missed in the pool of junk that showers you with jackpot wins and massive inheritance.
Though spam mails are often silly and non-threatening, some of them are scams and many users fall prey to these and end up losing their hard-earned money.
Today we’ll see the major techniques you can resort to block spam mails from getting into your inbox and disrupting your priority affairs.
What is SPAM mail?
To categorize a mail as spam or not, here are some symptoms you can look at, as specified by CAN–SPAM Act:
Mails with false or misleading header information
Deceptive subject lines and fraud content in mails
Sending advertisements without properly identifying
Mails without an option for recipients to opt out
Senders who do not honor opt-out requests promptly
Once you identify the type of mails to be avoided, you can block spam by following these precautions – both in user end and server side.
How to block spam mails from getting into your inbox
Today, we’ll see the best practices you can follow to block spam from an end-user level.
1. Block sender email address
Every email client have features to block a problematic sender email address. Usually this option to block a sender comes along with the mail itself.
For instance, in Outlook, when you no longer want to see messages from someone, you can block that sender by right-clicking the message and using the option ‘Junk > Block Sender’.
In Google mail, the mail drop down option contains the option to ‘Block Sender’, which can be used to prevent all mails from that account from reaching your inbox.
Block spam email sender
2. Never reply or click any links in spam mail
Spam mails should be ignored and not replied to. Also, caution should be exercised not to click the links or images in spam mail. Otherwise spammers will confirm that yours is a valid email account.
3. Unsubscribe from mailing lists
Many commonly visited sites such as online shopping, news sites, blogs, etc. require you to sign up in them, and you may unknowingly end up being in their mailing list or newsletters.
While some newsletters may be relevant, most of them would be advertisements which you don’t prefer to see. Unsubscribing from such lists helps to reduce unwanted mails from reaching your inbox.
4. Mark as spam
This is one of the most important feature to block spam. Every efficient mail server would have a Spam filter system in place, and its important that you make use of this feature to avoid spam mails.
Options in the email message, such as ‘Report Spam’, ‘Mark as Junk’, etc. can be used to train the Spam filter to identify that the mail is a spam and prevent it from hitting your inbox after that.
Mark a Spam mail as Junk
5. Caution in disclosing your email address
Care should be exercised regarding where you disclose your email address. Submitting it in almost all websites and locations is like inviting more spam mails to your account.
It is also advisable to use a secondary email address for trivial purposes like newsletter subscriptions or shopping sites and to reserve your primary email account for more priority mails.
6. Avoid default email addresses
Avoid using easy-to-guess email addresses. For instance, email ids such as “mary@mary.com” are easy to attract spammers and can end up receiving too many junk mails.
7. Monitor what others are doing on your behalf
When you authorize marketing or sales agencies for activities such as business promotions, you have to ensure that they don’t misuse your email address or account.
Not exercising adequate caution or control may land you in trouble. You may end up flooded with a lot of spam mails if you overlook such security aspects.
How to block spam mails in your server
While users can do their part to block spam mails in their email inbox, a server owner has to ensure that there are adequate measures in the mail server to avoid spam reaching your server.
Spamming to servers can cause mail queue to fill up, which can prevent valid email delivery or even crash your mail server. Its vital to prevent inbound spamming by following these measures.
1. Spam filters
Spam filters are software that are installed and configured along with your mail server to filter spam. They pick up the mails reaching the mail server and apply filters to them.
Only if the mails successfully pass the filters configured in the spam filter, they can reach the user’s inbox. All mails that are tagged as spam by the Spam filters are sent to the junk folder of the user’s mail account.
Users can examine the junk folder to see if there are any valid mails, and mark them as ‘Not junk’. If any spam mail escapes the filter, you can block that mail by marking it as Spam.
The most commonly used Spam filter are ‘Spamassassin’ and Mailscanner, and they can be configured alongside antivirus software such as ClamAV in mail servers such as Postfix, Exim, MailEnable, etc.
SpamAssassin to block spam
In SpamAssassin, the blacklisting option is a good way of training it to discard certain messages based on email addresses. From the configuration settings page, click the “Black list” -> “Add addresses”.
Enter all the email addresses from which you no longer wish to receive emails in the “Email addresses” field, and click OK. It will be a “No Entry” for those email addresses.
Block email address in SpamAssassin
By training the Spam filters by marking mails as Spam or ‘Not spam’, you can block spam mails effectively by about 90%, and thus reduce the burden caused to your users.
2. Lookup anti-spam records
Many spam mails are generated out of email spoofing. Spammers can take valid email addresses and send forged mails with ‘From’ addresses as those IDs, without really authenticating them.
Looking up sender domains for anti-spam records help to validate that the mails are originated from genuine senders and not spammers who spoof the email addresses.
Commonly configured anti-spam records are:
SPF (Sender Policy Framework) – SPF allows a domain owner to add a file or record on the server, that is specific to his domain name. Looking up and validating SPF of sender domains helps to avoid spoofed mails.
RDNS (Reverse DNS) – The reverse DNS record is setup for the hostname of the mail server to map to its IP address. If someone is trying to trick the mail server, the reverse DNS lookup will fail and that mail can be discarded.
DKIM (Domainkeys Identified Mail) – Domain key is an email authentication system. It is used to verify the domain of the email sender and to make sure that the message is not spam.
RDNS lookup
At Bobcares, we configure custom mail servers such as Postfix, Exim, Sendmail, etc. to validate emails with these anti-spam checks, thus avoiding spam mails from abusing the servers.
3. Use blacklists in mail server configuration
A blacklist, also known as DNSBL or RBL (DNS Blacklist or Realtime Blacklist), is a spam blocking list. If a mail server IP is listed in the blacklist, most mail servers reject mails from that IP.
SpamCop and SpamHaus are two famous DNS blacklisting companies. Users can submit spam mail senders to this blacklist. Configuring your mail server to lookup blacklists, avoid mails from those servers from reaching your server.
4. Block IPs
In some worst scenarios, where the spamming is out of control and cannot be prevented with spam filters alone, we resort to more security measures like blocking the IPs with firewalls, changing the mail server port, etc.
Conclusion
A few proactive and best practices at user end, coupled with a strong and effective Spam filter in mail server, can block spam mails from affecting your customers.
Bobcares helps online businesses of all sizes achieve world-class security and uptime, using tried and tested solutions. If you’d like to know how to make your mail servers secure and efficient, we’d be happy to talk to you.
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