POSTTLS-FINGER(1)                                            POSTTLS-FINGER(1)

       posttls-finger - Probe the TLS properties of an ESMTP or LMTP server.

       posttls-finger [options] [inet:]domain[:port] [match ...]
       posttls-finger -S [options] unix:pathname [match ...]

       posttls-finger(1)  connects  to  the  specified destination and reports
       TLS-related information about the server. With SMTP, the destination is
       a  domainname;  with LMTP it is either a domainname prefixed with inet:
       or a pathname prefixed with unix:.  If Postfix  is  built  without  TLS
       support, the resulting posttls-finger(1) program has very limited func-
       tionality, and only the -a, -c, -h, -o, -S, -t, -T and -v  options  are

       Note:  this is an unsupported test program. No attempt is made to main-
       tain compatibility between successive versions.

       For SMTP servers that don't support ESMTP, only the greeting banner and
       the  negative  EHLO response are reported. Otherwise, the reported EHLO
       response details further server capabilities.

       If TLS support is enabled when posttls-finger(1) is compiled,  and  the
       server supports STARTTLS, a TLS handshake is attempted.

       If  DNSSEC  support is available, the connection TLS security level (-l
       option) defaults to dane; see TLS_README  for  details.  Otherwise,  it
       defaults  to  secure.  This setting determines the certificate matching

       If TLS negotiation succeeds, the TLS protocol and  cipher  details  are
       reported.  The  server  certificate is then verified in accordance with
       the policy at the chosen (or  default)  security  level.   With  public
       CA-based  trust,  when  the  -L  option  includes  certmatch,  (true by
       default) name matching is performed even if the  certificate  chain  is
       not  trusted.  This logs the names found in the remote SMTP server cer-
       tificate and which if any  would  match,  were  the  certificate  chain

       Note:  posttls-finger(1) does not perform any table lookups, so the TLS
       policy table and obsolete per-site tables are not consulted.   It  does
       not  communicate  with  the tlsmgr(8) daemon (or any other Postfix dae-
       mons); its TLS session cache is held in private memory, and  disappears
       when the process exits.

       With  the  -r delay option, if the server assigns a TLS session id, the
       TLS session is cached. The connection  is  then  closed  and  re-opened
       after  the  specified delay, and posttls-finger(1) then reports whether
       the cached TLS session was re-used.

       When the destination is a load balancer, it may  be  distributing  load
       between  multiple  server  caches.  Typically,  each server returns its
       unique name in its EHLO response. If, upon reconnecting with -r, a  new
       server  name is detected, another session is cached for the new server,
       and the reconnect is repeated up to a maximum number of times  (default
       5) that can be specified via the -m option.

       The  choice  of  SMTP  or LMTP (-S option) determines the syntax of the
       destination argument. With  SMTP,  one  can  specify  a  service  on  a
       non-default  port  as host:service, and disable MX (mail exchanger) DNS
       lookups with [host] or [host]:port.  The [] form is required  when  you
       specify an IP address instead of a hostname.  An IPv6 address takes the
       form [ipv6:address].  The default port  for  SMTP  is  taken  from  the
       smtp/tcp  entry  in /etc/services, defaulting to 25 if the entry is not

       With LMTP, specify unix:pathname to connect to a local server listening
       on  a  unix-domain  socket  bound to the specified pathname; otherwise,
       specify an optional inet: prefix followed by a domain and  an  optional
       port,  with  the same syntax as for SMTP. The default TCP port for LMTP
       is 24.


       -a family (default: any)
              Address family preference: ipv4, ipv6 or any.  When  using  any,
              posttls-finger(1)  will  randomly  select  one of the two as the
              more preferred, and exhaust all MX  preferences  for  the  first
              address family before trying any addresses for the other.

       -A trust-anchor.pem (default: none)
              A  list of PEM trust-anchor files that overrides CAfile and CAp-
              ath trust chain verification.  Specify the option multiple times
              to  specify  multiple  files.  See the documentation for
              smtp_tls_trust_anchor_file for details.

       -c     Disable SMTP  chat  logging;  only  TLS-related  information  is

       -C     Print the remote SMTP server certificate trust chain in PEM for-
              mat.  The issuer DN, subject DN, certificate and public key fin-
              gerprints (see -d mdalg option below) are printed above each PEM
              certificate block.  If you specify -F CAfile or -P  CApath,  the
              OpenSSL  library  may augment the chain with missing issuer cer-
              tificates.  To see the actual chain  sent  by  the  remote  SMTP
              server leave CAfile and CApath unset.

       -d mdalg (default: $smtp_tls_fingerprint_digest)
              The  message  digest  algorithm to use for reporting remote SMTP
              server fingerprints and matching against user provided  certifi-
              cate fingerprints (with DANE TLSA records the algorithm is spec-
              ified in the DNS).   In  Postfix  versions  prior  to  3.6,  the
              default value was "md5".

       -f     Look  up  the associated DANE TLSA RRset even when a hostname is
              not an alias and its address records lie in  an  unsigned  zone.
              See smtp_tls_force_insecure_host_tlsa_lookup for details.

       -F CAfile.pem (default: none)
              The PEM formatted CAfile for remote SMTP server certificate ver-
              ification.  By default no CAfile is used and no public  CAs  are

       -g grade (default: medium)
              The  minimum  TLS  cipher  grade used by posttls-finger(1).  See
              smtp_tls_mandatory_ciphers for details.

       -h host_lookup (default: dns)
              The hostname lookup methods used for the  connection.   See  the
              documentation of smtp_host_lookup for syntax and semantics.

       -H chainfiles (default: none)
              List of files with a sequence PEM-encoded TLS client certificate
              chains.  The list can be built-up incrementally,  by  specifying
              the  option multiple times, or all at once via a comma or white-
              space separated list of filenames.  Each  chain  starts  with  a
              private  key, which is followed immediately by the corresponding
              certificate, and optionally by additional  issuer  certificates.
              Each new key begins a new chain for the corresponding algorithm.
              This option is mutually exclusive  with  the  below  -k  and  -K

       -k certfile (default: keyfile)
              File   with  PEM-encoded  TLS  client  certificate  chain.  This
              defaults to keyfile if one is specified.

       -K keyfile (default: certfile)
              File with PEM-encoded TLS client private key.  This defaults  to
              certfile if one is specified.

       -l level (default: dane or secure)
              The  security  level  for the connection, default dane or secure
              depending on whether DNSSEC is available.  For syntax and seman-
              tics,  see  the  documentation of smtp_tls_security_level.  When
              dane or dane-only is supported and selected, if no TLSA  records
              are  found,  or  all  the records found are unusable, the secure
              level will be used  instead.   The  fingerprint  security  level
              allows you to test certificate or public-key fingerprint matches
              before you deploy them in the policy table.

              Note, since posttls-finger(1)  does  not  actually  deliver  any
              email,  the  none,  may and encrypt security levels are not very
              useful.  Since may and encrypt don't require peer  certificates,
              they  will  often  negotiate  anonymous TLS ciphersuites, so you
              won't learn much about the remote SMTP server's certificates  at
              these  levels  if it also supports anonymous TLS (though you may
              learn that the server supports anonymous TLS).

       -L logopts (default: routine,certmatch)
              Fine-grained TLS logging  options.  To  tune  the  TLS  features
              logged during the TLS handshake, specify one or more of:

              0, none
                     These  yield  no TLS logging; you'll generally want more,
                     but this is handy if you just want the trust chain:
                     $ posttls-finger -cC -L none destination

              1, routine, summary
                     These synonymous values yield a normal  one-line  summary
                     of the TLS connection.

              2, debug
                     These synonymous values combine routine, ssl-debug, cache
                     and verbose.

              3, ssl-expert
                     These synonymous  values  combine  debug  with  ssl-hand-
                     shake-packet-dump.  For experts only.

              4, ssl-developer
                     These  synonymous values combine ssl-expert with ssl-ses-
                     sion-packet-dump.  For experts only, and in  most  cases,
                     use wireshark instead.

                     Turn  on OpenSSL logging of the progress of the SSL hand-

                     Log hexadecimal packet dumps of the  SSL  handshake;  for
                     experts only.

                     Log  hexadecimal  packet dumps of the entire SSL session;
                     only useful to those who can debug SSL protocol  problems
                     from hex dumps.

                     Logs  trust  chain verification problems.  This is turned
                     on automatically at security levels that use  peer  names
                     signed  by Certification Authorities to validate certifi-
                     cates.  So while this setting is recognized,  you  should
                     never need to set it explicitly.

                     This  logs  a  one line summary of the remote SMTP server
                     certificate subject, issuer, and fingerprints.

                     This logs remote SMTP server certificate matching,  show-
                     ing  the  CN  and  each  subjectAltName  and  which  name
                     matched.   With  DANE,  logs  matching  of  TLSA   record
                     trust-anchor and end-entity certificates.

              cache  This  logs session cache operations, showing whether ses-
                     sion caching is effective with the  remote  SMTP  server.
                     Automatically  used when reconnecting with the -r option;
                     rarely needs to be set explicitly.

                     Enables  verbose  logging  in  the  Postfix  TLS  driver;
                     includes all of peercert..cache and more.

              The  default  is routine,certmatch. After a reconnect, peercert,
              certmatch and verbose are automatically disabled while cache and
              summary are enabled.

       -m count (default: 5)
              When  the -r delay option is specified, the -m option determines
              the maximum number of reconnect attempts to use  with  a  server
              behind  a  load  balancer,  to see whether connection caching is
              likely to be effective for this destination.   Some  MTAs  don't
              expose  the  underlying  server identity in their EHLO response;
              with these servers there will never be more than 1  reconnection

       -M insecure_mx_policy (default: dane)
              The  TLS policy for MX hosts with "secure" TLSA records when the
              nexthop destination security level is dane, but  the  MX  record
              was found via an "insecure" MX lookup.  See the documen-
              tation for smtp_tls_dane_insecure_mx_policy for details.

       -o name=value
              Specify zero or more times to override the value of the
              parameter  name with value.  Possible use-cases include overrid-
              ing the values of TLS library  parameters,  or  "myhostname"  to
              configure the SMTP EHLO name sent to the remote server.

       -p protocols (default: >=TLSv1)
              TLS  protocols  that  posttls-finger(1) will exclude or include.
              See smtp_tls_mandatory_protocols for details.

       -P CApath/ (default: none)
              The OpenSSL CApath/  directory  (indexed  via  c_rehash(1))  for
              remote SMTP server certificate verification.  By default no CAp-
              ath is used and no public CAs are trusted.

       -r delay
              With a cacheable TLS session,  disconnect  and  reconnect  after
              delay seconds. Report whether the session is re-used. Retry if a
              new server is encountered, up to 5 times or  as  specified  with
              the  -m  option.  By default reconnection is disabled, specify a
              positive delay to enable this behavior.

       -R     Use SRV lookup instead of MX.

       -s servername
              The server name to send with  the  TLS  Server  Name  Indication
              (SNI)  extension.   When  the server has DANE TLSA records, this
              parameter is ignored and the TLSA base domain is  used  instead.
              Otherwise,  SNI  is  not  used by default, but can be enabled by
              specifying the desired value with this option.

       -S     Disable SMTP; that is, connect to an LMTP  server.  The  default
              port  for  LMTP over TCP is 24.  Alternative ports can specified
              by appending ":servicename" or ":portnumber" to the  destination

       -t timeout (default: 30)
              The TCP connection timeout to use.  This is also the timeout for
              reading the remote server's 220 banner.

       -T timeout (default: 30)
              The SMTP/LMTP command timeout for EHLO/LHLO, STARTTLS and  QUIT.

       -v     Enable  verbose  Postfix  logging.   Specify  more  than once to
              increase the level of verbose logging.

       -w     Enable outgoing TLS wrapper mode, or SUBMISSIONS/SMTPS  support.
              This  is typically provided on port 465 by servers that are com-
              patible with the SMTP-in-SSL protocol, rather than the  STARTTLS
              protocol.   The  destination  domain:port must of course provide
              such a service.

       -x     Prefer RFC7250 non-X.509 raw public  key  (RPK)  server  creden-
              tials.   By  default only X.509 certificates are accepted.  This
              is analogous to setting smtp_tls_enable_rpk = yes in the smtp(8)
              client.  At the fingerprint security level, when raw public keys
              are enabled, only public key (and not certificate)  fingerprints
              will  be compared against the specified list of match arguments.
              Certificate fingerprints are fragile when raw  public  keys  are
              solicited,  the server may at some point in time start returning
              only the public key.

       -X     Enable tlsproxy(8) mode. This is an unsupported mode,  for  pro-
              gram development only.

              Connect via TCP to domain domain, port port. The default port is
              smtp (or 24 with LMTP).  With SMTP an MX lookup is performed  to
              resolve  the  domain to a host, unless the domain is enclosed in
              [].  If you want to connect to a specific MX host, for  instance
    ,  specify  []  as the destination
              and as a match argument.  When using DNS, the desti-
              nation  domain  is assumed fully qualified and no default domain
              or search suffixes are applied;  you  must  use  fully-qualified
              names  or  also  enable native host lookups (these don't support
              dane or dane-only as no DNSSEC validation information is  avail-
              able via native lookups).

              Connect to the UNIX-domain socket at pathname. LMTP only.

       match ...
              With no match arguments specified, certificate peername matching
              uses the compiled-in default strategies for each security level.
              If  you specify one or more arguments, these will be used as the
              list of certificate or public-key digests to match for the  fin-
              gerprint level, or as the list of DNS names to match in the cer-
              tificate at the verify and secure levels.  If the security level
              is dane, or dane-only the match names are ignored, and hostname,
              nexthop strategies are used.

              Read configuration parameters from a non-default location.

              Same as -v option.

       smtp-source(1), SMTP/LMTP message source
       smtp-sink(1), SMTP/LMTP message dump

       TLS_README, Postfix STARTTLS howto

       The Secure Mailer license must be distributed with this software.

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       Viktor Dukhovni