.\"	$NetBSD: posttls-finger.1,v 1.4.2.1 2023/12/25 12:43:26 martin Exp $
.\"
.TH POSTTLS-FINGER 1 
.ad
.fi
.SH NAME
posttls-finger
\-
Probe the TLS properties of an ESMTP or LMTP server.
.SH "SYNOPSIS"
.na
.nf
\fBposttls\-finger\fR [\fIoptions\fR] [\fBinet:\fR]\fIdomain\fR[:\fIport\fR] [\fImatch ...\fR]
.br
\fBposttls\-finger\fR \-S [\fIoptions\fR] \fBunix:\fIpathname\fR [\fImatch ...\fR]
.SH DESCRIPTION
.ad
.fi
\fBposttls\-finger\fR(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 \fBinet:\fR or a pathname prefixed with \fBunix:\fR.  If
Postfix is built without TLS support, the resulting \fBposttls\-finger\fR(1)
program has very limited functionality, and only the \fB\-a\fR, \fB\-c\fR,
\fB\-h\fR, \fB\-o\fR, \fB\-S\fR, \fB\-t\fR, \fB\-T\fR and \fB\-v\fR options
are available.

Note: this is an unsupported test program. No attempt is made
to maintain 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 \fBposttls\-finger\fR(1) is compiled, and
the server supports \fBSTARTTLS\fR, a TLS handshake is attempted.

If DNSSEC support is available, the connection TLS security level
(\fB\-l\fR option) defaults to \fBdane\fR; see TLS_README for
details. Otherwise, it defaults to \fBsecure\fR.  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 \fB\-L\fR option includes \fBcertmatch\fR,
(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 certificate and which if any would match, were the certificate
chain trusted.

Note: \fBposttls\-finger\fR(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 \fBtlsmgr\fR(8) daemon (or any other
Postfix daemons); its TLS session cache is held in private memory, and
disappears when the process exits.

With the \fB\-r \fIdelay\fR 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 \fBposttls\-finger\fR(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
\fB\-r\fR, 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 \fB\-m\fR
option.

The choice of SMTP or LMTP (\fB\-S\fR option) determines the syntax of
the destination argument. With SMTP, one can specify a service on a
non\-default port as \fIhost\fR:\fIservice\fR, and disable MX (mail
exchanger) DNS lookups with [\fIhost\fR] or [\fIhost\fR]:\fIport\fR.
The [] form is required when you specify an IP address instead of a
hostname.  An IPv6 address takes the form [\fBipv6:\fIaddress\fR].
The default port for SMTP is taken from the \fBsmtp/tcp\fR entry in
/etc/services, defaulting to 25 if the entry is not found.

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

Arguments:
.IP "\fB\-a\fR \fIfamily\fR (default: \fBany\fR)"
Address family preference: \fBipv4\fR, \fBipv6\fR or \fBany\fR.  When
using \fBany\fR, \fBposttls\-finger\fR(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.
.IP "\fB\-A\fR \fItrust\-anchor.pem\fR (default: none)"
A list of PEM trust\-anchor files that overrides CAfile and CApath
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.
.IP "\fB\-c\fR"
Disable SMTP chat logging; only TLS\-related information is logged.
.IP "\fB\-C\fR"
Print the remote SMTP server certificate trust chain in PEM format.
The issuer DN, subject DN, certificate and public key fingerprints
(see \fB\-d \fImdalg\fR option below) are printed above each PEM
certificate block.  If you specify \fB\-F \fICAfile\fR or
\fB\-P \fICApath\fR, the OpenSSL library may augment the chain with
missing issuer certificates.  To see the actual chain sent by the
remote SMTP server leave \fICAfile\fR and \fICApath\fR unset.
.IP "\fB\-d \fImdalg\fR (default: \fB$smtp_tls_fingerprint_digest\fR)"
The message digest algorithm to use for reporting remote SMTP server
fingerprints and matching against user provided certificate
fingerprints (with DANE TLSA records the algorithm is specified
in the DNS).  In Postfix versions prior to 3.6, the default value
was "md5".
.IP "\fB\-f\fR"
Lookup 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.
.IP "\fB\-F \fICAfile.pem\fR (default: none)"
The PEM formatted CAfile for remote SMTP server certificate
verification.  By default no CAfile is used and no public CAs
are trusted.
.IP "\fB\-g \fIgrade\fR (default: medium)"
The minimum TLS cipher grade used by \fBposttls\-finger\fR(1).
See smtp_tls_mandatory_ciphers for details.
.IP "\fB\-h \fIhost_lookup\fR (default: \fBdns\fR)"
The hostname lookup methods used for the connection.  See the
documentation of smtp_host_lookup for syntax and semantics.
.IP "\fB\-H \fIchainfiles\fR (default: \fInone\fR)\fR"
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
whitespace 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 \fB\-k\fR and \fB\-K\fR options.
.IP "\fB\-k \fIcertfile\fR (default: \fIkeyfile\fR)\fR"
File with PEM\-encoded TLS client certificate chain. This
defaults to \fIkeyfile\fR if one is specified.
.IP "\fB\-K \fIkeyfile\fR (default: \fIcertfile\fR)"
File with PEM\-encoded TLS client private key.
This defaults to \fIcertfile\fR if one is specified.
.IP "\fB\-l \fIlevel\fR (default: \fBdane\fR or \fBsecure\fR)"
The security level for the connection, default \fBdane\fR or
\fBsecure\fR depending on whether DNSSEC is available.  For syntax
and semantics, see the documentation of smtp_tls_security_level.
When \fBdane\fR or \fBdane\-only\fR is supported and selected, if no
TLSA records are found, or all the records found are unusable, the
\fIsecure\fR level will be used instead.  The \fBfingerprint\fR
security level allows you to test certificate or public\-key
fingerprint matches before you deploy them in the policy table.
.IP
Note, since \fBposttls\-finger\fR(1) does not actually deliver any email,
the \fBnone\fR, \fBmay\fR and \fBencrypt\fR security levels are not
very useful.  Since \fBmay\fR and \fBencrypt\fR 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).
.IP "\fB\-L \fIlogopts\fR (default: \fBroutine,certmatch\fR)"
Fine\-grained TLS logging options. To tune the TLS features logged
during the TLS handshake, specify one or more of:
.RS
.IP "\fB0, none\fR"
These yield no TLS logging; you'll generally want more, but this
is handy if you just want the trust chain:
.RS
.ad
.nf
$ posttls\-finger \-cC \-L none destination
.fi
.RE
.IP "\fB1, routine, summary\fR"
These synonymous values yield a normal one\-line summary of the TLS
connection.
.IP "\fB2, debug\fR"
These synonymous values combine routine, ssl\-debug, cache and verbose.
.IP "\fB3, ssl\-expert\fR"
These synonymous values combine debug with ssl\-handshake\-packet\-dump.
For experts only.
.IP "\fB4, ssl\-developer\fR"
These synonymous values combine ssl\-expert with ssl\-session\-packet\-dump.
For experts only, and in most cases, use wireshark instead.
.IP "\fBssl\-debug\fR"
Turn on OpenSSL logging of the progress of the SSL handshake.
.IP "\fBssl\-handshake\-packet\-dump\fR"
Log hexadecimal packet dumps of the SSL handshake; for experts only.
.IP "\fBssl\-session\-packet\-dump\fR"
Log hexadecimal packet dumps of the entire SSL session; only useful
to those who can debug SSL protocol problems from hex dumps.
.IP "\fBuntrusted\fR"
Logs trust chain verification problems.  This is turned on
automatically at security levels that use peer names signed
by Certification Authorities to validate certificates.  So while
this setting is recognized, you should never need to set it
explicitly.
.IP "\fBpeercert\fR"
This logs a one line summary of the remote SMTP server certificate
subject, issuer, and fingerprints.
.IP "\fBcertmatch\fR"
This logs remote SMTP server certificate matching, showing the CN
and each subjectAltName and which name matched.  With DANE, logs
matching of TLSA record trust\-anchor and end\-entity certificates.
.IP "\fBcache\fR"
This logs session cache operations, showing whether session caching
is effective with the remote SMTP server.  Automatically used when
reconnecting with the \fB\-r\fR option; rarely needs to be set
explicitly.
.IP "\fBverbose\fR"
Enables verbose logging in the Postfix TLS driver; includes all of
peercert..cache and more.
.RE
.IP
The default is \fBroutine,certmatch\fR. After a reconnect,
\fBpeercert\fR, \fBcertmatch\fR and \fBverbose\fR are automatically
disabled while \fBcache\fR and \fBsummary\fR are enabled.
.IP "\fB\-m \fIcount\fR (default: \fB5\fR)"
When the \fB\-r \fIdelay\fR option is specified, the \fB\-m\fR 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.
.IP "\fB\-M \fIinsecure_mx_policy\fR (default: \fBdane\fR)"
The TLS policy for MX hosts with "secure" TLSA records when the
nexthop destination security level is \fBdane\fR, but the MX
record was found via an "insecure" MX lookup.  See the main.cf
documentation for smtp_tls_dane_insecure_mx_policy for details.
.IP "\fB\-o \fIname=value\fR"
Specify zero or more times to override the value of the main.cf
parameter \fIname\fR with \fIvalue\fR.  Possible use\-cases include
overriding the values of TLS library parameters, or "myhostname" to
configure the SMTP EHLO name sent to the remote server.
.IP "\fB\-p \fIprotocols\fR (default: >=TLSv1)"
TLS protocols that \fBposttls\-finger\fR(1) will exclude or include.  See
smtp_tls_mandatory_protocols for details.
.IP "\fB\-P \fICApath/\fR (default: none)"
The OpenSSL CApath/ directory (indexed via c_rehash(1)) for remote
SMTP server certificate verification.  By default no CApath is used
and no public CAs are trusted.
.IP "\fB\-r \fIdelay\fR"
With a cacheable TLS session, disconnect and reconnect after \fIdelay\fR
seconds. Report whether the session is re\-used. Retry if a new server
is encountered, up to 5 times or as specified with the \fB\-m\fR option.
By default reconnection is disabled, specify a positive delay to
enable this behavior.
.IP "\fB\-R\fR"
Use SRV lookup instead of MX.
.IP "\fB\-s \fIservername\fR"
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.
.IP "\fB\-S\fR"
Disable SMTP; that is, connect to an LMTP server. The default port for
LMTP over TCP is 24.  Alternative ports can specified by appending
"\fI:servicename\fR" or ":\fIportnumber\fR" to the destination
argument.
.IP "\fB\-t \fItimeout\fR (default: \fB30\fR)"
The TCP connection timeout to use.  This is also the timeout for
reading the remote server's 220 banner.
.IP "\fB\-T \fItimeout\fR (default: \fB30\fR)"
The SMTP/LMTP command timeout for EHLO/LHLO, STARTTLS and QUIT.
.IP "\fB\-v\fR"
Enable verbose Postfix logging.  Specify more than once to increase
the level of verbose logging.
.IP "\fB\-w\fR"
Enable outgoing TLS wrapper mode, or SUBMISSIONS/SMTPS support.  This
is typically provided on port 465 by servers that are compatible with
the SMTP\-in\-SSL protocol, rather than the STARTTLS protocol.
The destination \fIdomain\fR:\fIport\fR must of course provide such
a service.
.IP "\fB\-X\fR"
Enable \fBtlsproxy\fR(8) mode. This is an unsupported mode,
for program development only.
.IP "[\fBinet:\fR]\fIdomain\fR[:\fIport\fR]"
Connect via TCP to domain \fIdomain\fR, port \fIport\fR. The default
port is \fBsmtp\fR (or 24 with LMTP).  With SMTP an MX lookup is
performed to resolve the domain to a host, unless the domain is
enclosed in \fB[]\fR.  If you want to connect to a specific MX host,
for instance \fImx1.example.com\fR, specify [\fImx1.example.com\fR]
as the destination and \fIexample.com\fR as a \fBmatch\fR argument.
When using DNS, the destination domain is assumed fully qualified
and no default domain or search suffixes are applied; you must use
fully\-qualified names or also enable \fBnative\fR host lookups
(these don't support \fBdane\fR or \fBdane\-only\fR as no DNSSEC
validation information is available via \fBnative\fR lookups).
.IP "\fBunix:\fIpathname\fR"
Connect to the UNIX\-domain socket at \fIpathname\fR. LMTP only.
.IP "\fBmatch ...\fR"
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 \fBfingerprint\fR
level, or as the list of DNS names to match in the certificate at the
\fBverify\fR and \fBsecure\fR levels.  If the security level is
\fBdane\fR, or \fBdane\-only\fR the match names are ignored, and
\fBhostname, nexthop\fR strategies are used.
.ad
.fi
.SH "ENVIRONMENT"
.na
.nf
.ad
.fi
.IP \fBMAIL_CONFIG\fR
Read configuration parameters from a non\-default location.
.IP \fBMAIL_VERBOSE\fR
Same as \fB\-v\fR option.
.SH "SEE ALSO"
.na
.nf
smtp\-source(1), SMTP/LMTP message source
smtp\-sink(1), SMTP/LMTP message dump

.SH "README FILES"
.na
.nf
.ad
.fi
Use "\fBpostconf readme_directory\fR" or "\fBpostconf
html_directory\fR" to locate this information.
.na
.nf
TLS_README, Postfix STARTTLS howto
.SH "LICENSE"
.na
.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH "AUTHOR(S)"
.na
.nf
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