How do I block Postfix from sending spam?

Question

My postfix is sending spam from a [e-mail] address. How is this possible and how do I allow only www-data@localhost to send and postfix to only deliver from [e-mail] to [e-mail] (as in my aliases list)?

Here's my main.cf:

    # See /usr/share/postfix/main.cf.dist for a commented, more complete version


    # Debian specific:  Specifying a file name will cause the first
    # line of that file to be used as the name.  The Debian default
    # is /etc/mailname.
    #myorigin = *** My main domain ***

    smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
    biff = no

    # appending .domain is the MUA's job.
    append_dot_mydomain = no

    # Uncomment the next line to generate "delayed mail" warnings
    #delay_warning_time = 4h

    readme_directory = no

    # TLS parameters
    smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
    smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
    smtpd_use_tls=yes
    smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
    smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

    # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
    # information on enabling SSL in the smtp client.

    myhostname = *** My hostname ***
    alias_maps = hash:/etc/aliases
    alias_database = hash:/etc/aliases
    myorigin = $mydomain
    mydestination = $myhostname, localhost.$mydomain, $mydomain, localhost
    mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
    mailbox_size_limit = 0
    recipient_delimiter = +
    smtpd_sasl_auth_enable = yes
    smtpd_sasl_security_options = noanonymous noplaintext
    smtpd_recipient_restrictions = permit_mynetworks reject_unauth_destination permit_inet_interfaces
    smtpd_tls_security_level = may

    virtual_alias_domains = *** My aliases ***
    virtual_alias_maps = hash:/etc/postfix/virtual
    smtpd_tls_auth_only = yes


smtpd_client_restrictions = permit_mynetworks, reject
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination, permit
smtpd_data_restrictions = reject_unauth_pipelining
smtpd_end_of_data_restrictions = check_policy_service unix:private/policy
smtp_sasl_auth_enable = no
smtpd_sender_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_non_fqdn_sender, reject_unknown_sender_domain, hash:/etc/postfix/sender_access, permit
smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks, check_helo_access hash:/etc/postfix/sender_access, reject_non_fqdn_hostname, reject_invalid_hostname, permit
smtpd_recipient_restrictions = reject_unauth_pipelining, reject_unauth_destination, reject_non_fqdn_recipient, permit_mynetworks, permit_sasl_authenticated, check_sender_access hash:/etc/postfix/sender_access, reject_rbl_client relays.ordb.org, reject_rbl_client list.dsbl.org, reject_rbl_client sbl-xbl.spamhaus.org, check_policy_service unix:private/spfpolicy, check_policy_service inet:127.0.0.1:10023, permit
transport_maps = hash:/etc/postfix/transport

Answer 1

See if setting relay_recipient_maps properly fixes it.

I think this is the problem...

You are right to set reject_unauth_destination, but the server basically doesn't have explicit instructions on what an "unauth destination" actually is. If it's not an account or forward on your machine, it should not be authorized to relay unless it a sasl authentication or a permitted network machine.

Spammers are sending forged messages to your machine, which is unable to deliver them to non-existent accounts. Since it can't tell whether they are "unauth" desintations, it attempts to treat them as legit SMTP errors but not as unauthorized and, therefore, sends the error back to the "originating" MTA (which is either forged or misconfigured).

On a properly configured mail server, deferrals should be pretty unusual. If you feel safe doing it, and are sure that you won't delete anything legitimate, run postsuper -d ALL deferred to delete all deferred mail in queue. If I'm right, the queue shouldn't fill up like that again. for