Postfix manual - posttls-finger(1)

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

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

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

    DESCRIPTION
           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, -S,  -t,  -T  and  -v  options  are
           available.

           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
           policy.

           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
           trusted.

           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
           found.

           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.

           Arguments:

           -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 main.cf documentation for
                  smtp_tls_trust_anchor_file for details.

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

           -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
                  trusted.

           -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
                  options.

           -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.

                  ssl-debug
                         Turn  on OpenSSL logging of the progress of the SSL hand-
                         shake.  This includes detailed output  of  decoded  hand-
                         shake messages.

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

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

                  trace  Available  with  Postfix  3.12   and   later.   Write   a
                         human-readable  protocol transcript of the TLS session to
                         a file in  the  current  directory.  The  file  is  named
                         process_name-date_time.usec-peer-XXXXXX,  where XXXXXX is
                         replaced with a unique  string  to  avoid  filename  con-
                         flicts.  All  reconnect attempts in a single command-line
                         run share the same trace file, separated  by  "===  post-
                         tls-finger  reconnect  ==="  lines. When -X is in effect,
                         tlsproxy(8) generates the trace file under  $queue_direc-
                         tory/tlstrace/  instead.  The  keyword  is ignored with a
                         warning if Postfix or OpenSSL was built without TLS trace
                         support.

                  untrusted
                         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.

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

                  certmatch
                         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.

                  verbose
                         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
                  attempt.

           -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 main.cf 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  main.cf
                  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
                  argument.

           -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.

           [inet:]domain[:port]
                  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
                  mx1.example.com,  specify  [mx1.example.com]  as the destination
                  and example.com 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).

           unix:pathname
                  Connect  to  the  UNIX-domain  socket  at pathname. This feature
                  requires "-S".

           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.

    ENVIRONMENT
           MAIL_CONFIG
                  Read configuration parameters from a non-default location.

           MAIL_VERBOSE
                  Same as -v option.

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

    README FILES
           TLS_README, Postfix STARTTLS howto

    LICENSE
           The Secure Mailer license must be distributed with this software.

    AUTHOR(S)
           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

                                                                 POSTTLS-FINGER(1)