Outgoing email marked as spam: BAYES_99

Question

I am developing a web application.
All outgoing emails are marked as spam, or totally rejected by receivers' email providers.
This prevents us from sending welcome emails, activation codes, or anything else to registered users.

I tested my email sending with isnotspam.com, and the problem seems to be the BAYES_99 and BAYES_999 metrics. This happens regardless of email content.

Can someone tell me why this is happening? Is there a way to make outgoing emails not marked as spam by spam filters?

Here the outcome of a isnotspam.com test result (I modified a few parameters for privacy ).

    This message is an automatic response from isNOTspam's authentication verifier service. The service allows email senders to perform a simple check of various sender authentication mechanisms. It is provided free of charge, in the hope that it is useful to the email community. While it is not officially supported, we welcome any feedback you may have at .

    Thank you for using isNOTspam.

    The isNOTspam team

    ==========================================================
    Summary of Results
    ==========================================================

    SPF Check : pass
    Sender-ID Check : pass
    DomainKeys Check : neutral
    DKIM Check : pass
    SpamAssassin Check : ham (non-spam)
    ==========================================================
    Details:
    ==========================================================

    HELO hostname: my.hostname.com
    Source IP: XX.YY.WW.ZZ
    mail-from: [email protected]
    Anonymous To: [email protected]
    ---------------------------------------------------------
    SPF check details:
    ----------------------------------------------------------

    Result: pass
    ID(s) verified: [email protected]
    DNS record(s):
    mydomain.com.    11379   IN      TXT     "v=spf1 +a +mx +ip4:XX.YY.WW.ZZ +ip4:AA.BB.CC.DD +include:_spf.google.com ~all"


    ----------------------------------------------------------
    Sender-ID check details:
    ----------------------------------------------------------

    Result: pass

    ID(s) verified: [email protected]
    DNS record(s):
    mydomain.com.    11379   IN      TXT     "v=spf1 +a +mx +ip4:XX.YY.WW.ZZ +ip4:AA.BB.CC.DD +include:_spf.google.com ~all"


    ----------------------------------------------------------
    DomainKeys check details:
    ----------------------------------------------------------

    Result: neutral (message not signed)
    ID(s) verified: [email protected]
    Selector=
    domain=
    DomainKeys DNS Record=

    ----------------------------------------------------------
    DKIM check details:
    ----------------------------------------------------------

    Result: pass
    ID(s) verified: [email protected]
    Selector=default
    domain=mydomain.com

    DomainKeys DNS Record=default._domainkey.mydomain.com


    ----------------------------------------------------------
    SpamAssassin check details:
    ----------------------------------------------------------
    SpamAssassin 3.4.1 (2015-04-28)

    Result: ham (non-spam) (03.7points, 10.0 required)

    pts rule name description
    ---- ---------------------- -------------------------------


    * 3.5 BAYES_99 BODY: Bayes spam probability is 99 to 100%
    * [score: 1.0000]
    * 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked.
    * See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block
    * for more information.
    * [URIs: mydomain.com]
    * -0.0 SPF_HELO_PASS SPF: HELO matches SPF record
    * -0.0 SPF_PASS SPF: sender matches SPF record
    * 0.2 BAYES_999 BODY: Bayes spam probability is 99.9 to 100%
    * [score: 1.0000]
    * 0.1 HTML_MESSAGE BODY: HTML included in message
    * -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's
    * domain
    * -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature
    * 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily
    * valid
    X-Spam-Status: Yes, hits=3.7 required=-20.0 tests=BAYES_99,BAYES_999,
    DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HTML_MESSAGE,SPF_HELO_PASS,SPF_PASS,
    URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.1
    X-Spam-Score: 3.7

Answer 1

I posted this question in total panic, our company was having trouble while launching a new product, customers were dissatisfied and we were struggling finding what the problem was.

In the end, our emails were not received not because of spam detection, but because of an error in our server configuration. There were conditions that caused emails to not be sent at all.

Key takeaway from this story is: if you have problems sending emails, verify that you are sending valid html (through validator.w3.org for example) and check your server configuration before thinking about spam.