SMTP Module

The smtp module can perform two actions:

When called in the authenticate section, it validates a users name and password from request attributes against an SMTP server without sending a mail.

When called with the method mail it will send an email.

The module can optionally perform a tls handshake, enabled with require_cert

tls { … }: Configure the tls related items which control how FreeRADIUS connects to an SMTP server.

Certificate validation options

Specifies how the certificate(s) presented by the SMTP server are validated, and which certificates (if any) to send to that SMTP server.

The options here behave the same as the options in other tls sections in the server.

certificate_file: PEM formatted file containing the certificate we present to the SMTP server

Specifies a certificate and any intermediary CAs we should send to the SMTP server.

This file should usually contain the client certificate file first, then any intermediary signing CAs, shallowest (direct signee of the certificate_file) to deepest (signed directly by the root CA).

ca_file: PEM formatted file containing the chain to validate the SMTP server’s certificate.

Any certificate chain MUST be in order from server certificate (first in the file) to intermediary CAs (second) to Root CA (last in the file) as per RFC 4346 Section 7.4.2 (see certificate_list)

Providing a complete certificate chain here is the most common way of validating the certificate presented by an SMTP server.

ca_issuer_file: PEM formatted file containing the CA that signed the SMTP server’s certificate.

Specifies the certificate which directly signed the certificate presented by the SMTPs server.

This configuration option can be used to prevent certificates passing validation which were signed by other intermediary CAs, or root CAs, in the trusted certificate chain.

ca_path: A directory containing multiple root CA certs named by their hash.

See the OpenSSL documentation for more details: - https://www.openssl.org/docs/man1.1.0/man3/SSL_CTX_set_default_verify_paths.html - https://www.openssl.org/docs/man1.1.1/man1/c_rehash.html

This configuration option should only be used when the SMTP server being contacted is not known ahead of time (using a URL from an external source), and/or the CA used to sign the SMTP server certificate is unknown.

If not set, then whatever libcurl has as its default will be used, which typically will be the operating system’s set of trusted CAs. This will be visible in the debug output when FreeRADIUS starts.

private_key_file: PEM formatted file containing the private key for the specified certificate_file

This item must be specified if certificate_file is being used.

private_key_password: Password used to decrypt the private_key_file.
random_file: Source of random data used for various cryptographic functions.
check_cert: Server certificate verification requirements.

May be one of:

Option Description

Option	Description
`no`	Server certificate can be signed by any CA or be self-signed.
`yes`	Server certificate must be issued by one of the trusted CAs.

no

Server certificate can be signed by any CA or be self-signed.

yes

Server certificate must be issued by one of the trusted CAs.

Default is yes

request_cert: Options for controlling how the module requests TLS to the SMTP server.

May be one of:

Option Description

Option	Description
`demand`	Require ssl validation to accept login
`never`	Do not try to establish ssl connection
`allow`	Try to establish ssl connection, continue even if it cannot

demand

Require ssl validation to accept login

never

Do not try to establish ssl connection

allow

Try to establish ssl connection, continue even if it cannot

default is 'allow'

check_cert_cn: Server certificate CN verification requirements.

May be one of:

Option Description

Option	Description
`no`	Server certificate CN can be any value.
`yes`	Server certificate CN matches the host in the URI.

no

Server certificate CN can be any value.

yes

Server certificate CN matches the host in the URI.

Default is yes

extract_cert_attrs: Extract OIDs from presented certificates as OIDs.

Default is no

uri: URI which will be used for connecting to the SMTP server.

The smtp module uses Curl (https://curl.haxx.se/libcurl/) to implement the underlying mail protocols. The URI should be in the form of:

SCHEME://IP:PORT/

SCHEME can be one of the SMTP protocols supported by Curl. i.e. smtp, smtps. If no SCHEME is given, it defaults to smtp.

IP is the IP address of the server. It can be an IPv4 address, IPv6 address, hostname, etc.

PORT is optional, and will normally be chosen to be correct for the given SCHEME.

For more information, see the CURL documentation at

https://ec.haxx.se/cmdline/cmdline-urls

timeout: How long the module will wait before giving up on the response from the SMTP server.
username_attribute: Which attribute in the request should be used as the user’s username when performing SMTP authentication.
password_attribute: Which attribute in the request should be used as the user’s password when performing SMTP authentication.
username: User name to use when sending emails. Can be a fixed string or an attribute. Leave unset if authentication is not required to send emails.
password: Password to use in conjunction with the above user name for SMTP authentication.
template_directory: The source directory where all file attachments are pulled from All file attachments should be their relative path from this location, without a leading /
Attachments: attachments with their relative path from template_directory There can be no leading / or ..
envelope_address: This is the address used to send the mail, Sent to the receiving server as MAIL FROM:<envelope_address> sender_address will be defaulted to if this is not set
sender_address: This are the addresses displayed in the FROM: element of the header This can be different than the provided envelope_address, If envelope_address is set, this can be formatted however you want it to appear to the receiver If envelope_address is not set, the first element in sender_address will be used as the envelope address
recipients: Email addresses to be set as recipients for the email If recipients is set bcc, cc, and to will not be automatically added to the email And so they must be included here.
to: Email addresses to be set in the TO: header These addresses will be added as envelope recipients only if recipients is not set
cc: Email addresses to be set in the CC: header These addresses will be added as envelope recipients only if recipients is not set
bcc: Comma separated list of emails. the local part may contain commas, the domain may not (RFC 2821) Therefore, first comma after the @ represents a new address not listed in the header of the email if recipients is not set, these emails will be added to the envelope recipients
set_date: Adds a Date: to the header, set to the time the request is received Formatted as "Fri, 07 Aug 2020 00:57:37 -0400, (EDT)" May be one of:

Option Description

Option	Description
`no`	A Date: should be specified in the header, or left to the receiving mta
`yes`	A Date is formatted and added (recommended)

no

A Date: should be specified in the header, or left to the receiving mta

yes

A Date is formatted and added (recommended)

Default is yes

header: This is where any other headers can be added to the email FROM, TO, and CC, should not be added here if their respective elements were set in the config If no DATE header is provided, one will be added showing time that the request was received(recommended) Non-standard mail headers may be set. Adhere to your MTA’s documentation
connection { .. }: Configure how connection handles are managed per thread.

Reusable connection handles are allocated in blocks. These parameters allow for tuning how that is done.

Since http requests are performed async, the settings here represent outstanding http requests per thread.

min: The minimum number of connection handles to keep allocated.
max: The maximum number of reusable connection handles to allocate.

Any requests to allocate a connection handle beyond this number will cause a temporary handle to be allocated. This is less efficient than the block allocation so max should be set to reflect the number of outstanding requests expected at peak load.

cleanup_interval: How often to free un-used connection handles.

Every cleanup_interval a cleanup routine runs which will free any blocks of handles which are not in use, ensuring that at least min handles are kept.

Default Configuration

smtp {
	tls {
#		certificate_file     = /path/to/radius.pem
#		ca_file	             = "${certdir}/cacert.pem"
#		ca_issuer_file     = "${certdir}/caissuer.pem"
#		ca_path	             = "${certdir}"
#		private_key_file     = /path/to/radius.key
#		private_key_password = "supersecret"
#		random_file          = /dev/urandom
#		check_cert = no
#		require_cert = allow
#		check_cert_cn = no
#		extract_cert_attrs = no
	}
	uri = "smtp://192.0.20.1/"
	timeout = 5s
#	username_attribute = &User-Name
#	password_attribute = &User-Password
#	username = "user"
#	password = "secret"
	template_directory = raddb/mods_config/smtp
	attachments = &SMTP-Attachments[*]
	envelope_address = "postmaster@localhost"
	sender_address = &SMTP-Sender-Address[*]
#	recipients = &SMTP-Recipients[*]
#	recipients = &SMTP-TO[*]
#	recipients = &SMTP-CC[*]
#	recipients = &SMTP-BCC[*]
#	to = &SMTP-TO[*]
#	cc = &SMTP-CC[*]
#	bcc = &SMTP-BCC[*]
#	set_date = yes
	header {
		subject = "email subject"
		Message-ID = "950124.162336@example.com"
#		X-Originating-IP = "192.0.20.1"
	}
	connection {
		reuse {
			min = 10
			max = 100
			cleanup_interval = 30s
		}
	}
}