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How does Business Mail filter spam?

Worried about Spam? Leave it all behind with Business Mail!

Business Mail uses various filters and measures to keep your inbox clean, which are given below:

  • Postscreen: This is a filter we use that helps us detect if an incoming email is from a spambot or if it contains malware. An email is rejected from delivery if it fails this check.
  • Sender check: This component detects if the received email has been sent by a valid email server. Sender check will essentially perform a reverse DNS lookup to figure out what is the IP of the received email. If the IP does not point to a valid email server, the email in question will be rejected.

  • SPF (Sender Policy Framework) check: This component will check the SPF record of the sender domain and validate whether the email is coming from a valid server as mentioned in the SPF record . If the mail is received from an unauthenticated source, the SPF check will perform the action mentioned in the sender domain’s TXT record accordingly as given below:
    1. Hard Fail : The email will be rejected by our servers if it is received from an unauthenticated source
    2. Soft Fail : The email will be accepted by our servers, but it will be tagged as ‘suspicious’ and the recipient will be warned

  • RBL (Real-time Blackhole List) check: The IP address of an incoming email is run by 2-3 RBL services to verify if the IP has been blacklisted before due to being identified as spammy in nature. Hence. the incoming email will be rejected if the IP is blacklisted.
  • Open DKIM (DomainKeys Identified Mail) check: If an incoming email's header contains the DKIM Signature, an Open DKIM check will verify the content of the email with the public key published in the DNS record and add the verification result in the Authentication-Results header.

  • Open DMARC (Domain-based Message Authentication, Reporting & Conformance) check: Open DMARC check will check the status of SPF and Open DKIM checks. Incoming emails will be rejected if they fail the DMARC check, or temporarily failed if the check could not be completed in time. It will add the verification result in the Authentication-Results header

  • Cmfilter: Cmfilter essentially checks if an incoming email is a spam, virus, or phishing email. If it is a virus email or if it is from a spam IP, then it will be rejected. The process for the same is given below:

a. It compares the sender IP to a set of known spammy hosts and rejects if the email is received from a spammy host

b. Cmfilter contains a cache of all signatures that have a known classification. It generates the signatures of an incoming message and compares them with known signatures and classifies them into different categories which are given below:

      1. Spam :
        1. Incoming Spam email will get delivered to the spam folder and the subject will be tagged as SPAM
        2. Outgoing spam emails will get rejected
      2. Virus : Email with virus content will be rejected
      3. Phishing : The subject will be tagged as PHISHING
  • Clam SMTP (Simple Mail Transfer Protocol) filter: Clam SMTP filter allows checking for viruses using the ClamAV anti-virus software. Emails with viruses are dropped silently and logged without any additional action taken.
  • MIME (Multimedia Internet Mail Extensions) header check: MIME header check will essentially check the attachments that have been added to the email. If the file extension format isn't permitted by the incoming email server then the email will be rejected.
An incoming email is delivered to your mailbox only after passing through all the above-mentioned checks and filters.


If you have any queries or face any difficulties, please feel free to write to us at We shall be happy to help!

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