Distributed James Server — smtpserver.xml

Incoming SMTP

Consult this example to get some examples and hints.

The SMTP service is controlled by a configuration block in the smptserver.xml. The smtpserver tag defines the boundaries of the configuration block. It encloses all the relevant configuration for the SMTP server. The behavior of the SMTP service is controlled by the attributes and children of this tag.

This tag has an optional boolean attribute - enabled - that defines whether the service is active or not. The value defaults to "true" if not present.

The standard children of the smtpserver tag are:

Table 1. smtpserver.xml content
Property name	explanation
bind	A list of address:port separed by comma - This is an optional value. If present, this value is a string describing the IP address to which this service should be bound. If the tag or value is absent then the service will bind to all network interfaces for the machine on port 25. Port 25 is the well-known/IANA registered port for SMTP. Port 465 is the well-known/IANA registered port for SMTP over TLS.
connectBacklog	The IP address (host name) the MBean Server will bind/listen to.
tls	Set to true to support STARTTLS or SSL for the Socket. To use this you need to copy sunjce_provider.jar to /path/james/lib directory. To create a new keystore execute: `keytool -genkey -alias james -keyalg RSA -storetype PKCS12 -keystore /path/to/james/conf/keystore`. The algorithm is optional and only needs to be specified when using something other than the Sun JCE provider - You could use IbmX509 with IBM Java runtime. Please note that each SMTP/LMTP server exposed on different port can specify its own keystore, independently from any other TLS based protocols.
helloName	This is a required tag with an optional body that defines the server name used in the initial service greeting. The tag may have an optional attribute - autodetect. If the autodetect attribute is present and true, the service will use the local hostname returned by the Java libraries. If autodetect is absent or false, the body of the tag will be used. In this case, if nobody is present, the value "localhost" will be used.
connectionTimeout	This is an optional tag with a non-negative integer body. Connection timeout in seconds.
connectionLimit	Set the maximum simultaneous incoming connections for this service.
connectionLimitPerIP	Set the maximum simultaneous incoming connections per IP for this service.
proxyRequired	Enables proxy support for this service for incoming connections. HAProxy’s protocol (https://www.haproxy.org/download/2.7/doc/proxy-protocol.txt) is used and might be compatible with other proxies (e.g. traefik). If enabled, it is required to initiate the connection using HAProxy’s proxy protocol.
authRequired	(deprecated) use auth.announce instead. This is an optional tag with a boolean body. If true, then the server will announce authentication after HELO command. If this tag is absent, or the value is false then the client will not be prompted for authentication. Only simple user/password authentication is supported at this time. Supported values: * true: announced only to not authorizedAddresses * false: don’t announce AUTH. If absent, authorizedAddresses are set to a wildcard to accept all remote hosts. * announce: like true, but always announce AUTH capability to clients Please note that emails are only relayed if, and only if, the user did authenticate, or is in an authorized network, regardless of this option.
auth.announce	This is an optional tag. Possible values are: * never: Don’t announce auth. * always: always announce AUTH capability to clients. * forUnauthorizedAddresses: announced only to not authorizedAddresses Please note that emails are only relayed if, and only if, the user did authenticate, or is in an authorized network, regardless of this option.
auth.requireSSL	This is an optional tag, defaults to true. If true, authentication is not advertised via capabilities on unencrypted channels.
auth.plainAuthEnabled	This is an optional tag, defaults to true. If false, AUTH PLAIN and AUTH LOGIN will not be exposed. This setting can be used to enforce strong authentication mechanisms.
auth.oidc.oidcConfigurationURL	Provide OIDC url address for information to user. Only configure this when you want to authenticate SMTP server using a OIDC provider.
auth.oidc.jwksURL	Provide url to get OIDC’s JSON Web Key Set to validate user token. Only configure this when you want to authenticate SMTP server using a OIDC provider.
auth.oidc.claim	Claim string uses to identify user. E.g: "email_address". Only configure this when you want to authenticate SMTP server using a OIDC provider.
auth.oidc.scope	An OAuth scope that is valid to access the service (RF: RFC7628). Only configure this when you want to authenticate SMTP server using a OIDC provider.
auth.oidc.introspection.url	Optional. An OAuth introspection token URL will be called to validate the token (RF: RFC7662). Only configure this when you want to validate the revocation token by the OIDC provider. Note that James always verifies the signature of the token even whether this configuration is provided or not.
auth.oidc.introspection.auth	Optional. Provide Authorization in header request when introspecting token. Eg: `Basic xyz`
auth.oidc.userinfo.url	Optional. An Userinfo URL will be called to validate the token (RF: OpenId.Core https://openid.net/specs/openid-connect-core-1_0.html). Only configure this when you want to validate the revocation token by the OIDC provider. Note that James always verifies the signature of the token even whether this configuration is provided or not. James will ignore check token by userInfo if the `auth.oidc.introspection.url` is already configured
authorizedAddresses	Authorize specific addresses/networks. If you use SMTP AUTH, addresses that match those specified here will be permitted to relay without SMTP AUTH. If you do not use SMTP AUTH, and you specify addresses here, then only addresses that match those specified will be permitted to relay. Addresses may be specified as a IP address or domain name, with an optional netmask, e.g., 127.*, 127.0.0.0/8, 127.0.0.0/255.0.0.0, and localhost/8 are all the same See also the RemoteAddrNotInNetwork matcher in the transport processor. You would generally use one OR the other approach.
verifyIdentity	This is an optional tag with a boolean body. This option can only be used if SMTP authentication is required. If the parameter is set to true then the sender address for the submitted message will be verified against the authenticated subject. Verify sender addresses, ensuring that the sender address matches the user who has authenticated. It will verify that the sender address matches the address of the user or one of its alias (from user or domain aliases). This prevents a user of your mail server from acting as someone else If unspecified, default value is true.
maxmessagesize	This is an optional tag with a non-negative integer body. It specifies the maximum size, in kbytes, of any message that will be transmitted by this SMTP server. It is a service-wide, as opposed to a per user, limit. If the value is zero then there is no limit. If the tag isn’t specified, the service will default to an unlimited message size. Must be a positive integer, optionally with a unit: B, K, M, G.
heloEhloEnforcement	This sets whether to enforce the use of HELO/EHLO salutation before a MAIL command is accepted. If unspecified, the value defaults to true.
smtpGreeting	This sets the SMTPGreeting which will be used when connect to the smtpserver If none is specified a default is generated
handlerchain	The configuration handler chain. See this page for configuring out-of the box extra SMTP handlers and hooks.
bossWorkerCount	Set the maximum count of boss threads. Boss threads are responsible for accepting incoming SMTP connections and initializing associated resources. Optional integer, by default, boss threads are not used and this responsibility is being dealt with by IO threads.
ioWorkerCount	Set the maximum count of IO threads. IO threads are responsible for receiving incoming SMTP messages and framing them (split line by line). IO threads also take care of compression and SSL encryption. Their tasks are short-lived and non-blocking. Optional integer, defaults to 2 times the count of CPUs.
maxExecutorCount	Set the maximum count of worker threads. Worker threads takes care of potentially blocking tasks like executing SMTP commands. Optional integer, defaults to 16.

OIDC setup

James SMTP support XOAUTH2 authentication mechanism which allow authenticating against a OIDC providers. Please configure auth.oidc part to use this.

We do supply an example of such a setup. It uses the Keycloak OIDC provider, but usage of similar technologies is definitely doable.

About open relays

Authenticated SMTP is a method of securing your SMTP server. With SMTP AUTH enabled senders who wish to relay mail through the SMTP server (that is, send mail that is eventually to be delivered to another SMTP server) must authenticate themselves to Apache James Server before sending their message. Mail that is to be delivered locally does not require authentication. This method ensures that spammers cannot use your SMTP server to send unauthorized mail, while still enabling users who may not have fixed IP addresses to send their messages.

Mail servers that allow spammers to send unauthorized email are known as open relays. So SMTP AUTH is a mechanism for ensuring that your server is not an open relay.

It is extremely important that your server not be configured as an open relay. Aside from potential costs associated with usage by spammers, connections from servers that are determined to be open relays are routinely rejected by SMTP servers. This can severely impede the ability of your mail server to send mail.

At this time Apache James Server only supports simple user name / password authentication.

As mentioned above, SMTP AUTH requires that Apache James Server be able to distinguish between mail intended for local delivery and mail intended for remote delivery. Apache James Server makes this determination by matching the domain to which the mail was sent against the DomainList component, configured by domainlist.xml.

The Distributed Server is configured out of the box so as to not serve as an open relay for spammers. This is done by relayed emails originate from a trusted source. This includes:

Authenticated SMTP/JMAP users
Mails generated by the server (eg: bounces)
Mails originating from a trusted network as configured in smtpserver.xml

If you wish to ensure that authenticated users can only send email from their own account, you may optionally set the verifyIdentity element of the smtpserver configuration block to "true".

Verification

Verify that you have not inadvertently configured your server as an open relay. This is most easily accomplished by using the service provided at mxtoolbox.com. mxtoolbox.com will check your mail server and inform you if it is an open relay. This tool further more verifies additional properties like:

Your DNS configuration, especially that you mail server IP has a valid reverse DNS entry
That your SMTP connection is secured
That you are not an OpenRelay
This website also allow a quick lookup to ensure your mail server is not in public blacklists.

Of course it is also necessary to confirm that users and log in and send mail through your server. This can be accomplished using any standard mail client (i.e. Thunderbird, Outlook, Eudora, Evolution).

LMTP Configuration

Consult this example to get some examples and hints.

The configuration is the same of for SMTP.

By default, it is deactivated. You can activate it alongside SMTP and bind for example on port 24.

The default LMTP server stores directly emails in user mailboxes, without further treatment.

However we do ship an alternative handler chain allowing to execute the mailet container, thus achieving a behaviour similar to the default SMTP protocol. Here is how to achieve this:

<lmtpservers>
    <lmtpserver enabled="true">
        <jmxName>lmtpserver</jmxName>
        <bind>0.0.0.0:24</bind>
        <connectionBacklog>200</connectionBacklog>
        <connectiontimeout>1200</connectiontimeout>
        <connectionLimit>0</connectionLimit>
        <connectionLimitPerIP>0</connectionLimitPerIP>
        <maxmessagesize>0</maxmessagesize>
        <handlerchain coreHandlersPackage="org.apache.james.lmtpserver.MailetContainerCmdHandlerLoader">
            <handler class="org.apache.james.lmtpserver.MailetContainerCmdHandlerLoader"/>
        </handlerchain>
    </lmtpserver>
</lmtpservers>

Note that by default the mailet container is executed with all recipients at once and do not allow per recipient error reporting. An option <code>splitExecution</code> allow to execute the mailet container for each recipient separately and mitigate this limitation at the cost of performance.

<lmtpservers>
    <lmtpserver enabled="true">
        <jmxName>lmtpserver</jmxName>
        <bind>0.0.0.0:24</bind>
        <connectionBacklog>200</connectionBacklog>
        <connectiontimeout>1200</connectiontimeout>
        <connectionLimit>0</connectionLimit>
        <connectionLimitPerIP>0</connectionLimitPerIP>
        <maxmessagesize>0</maxmessagesize>
        <handlerchain coreHandlersPackage="org.apache.james.lmtpserver.MailetContainerCmdHandlerLoader">
            <handler class="org.apache.james.lmtpserver.MailetContainerCmdHandlerLoader"/>
            <handler class="org.apache.james.lmtpserver.MailetContainerHandler">
                <splitExecution>true</splitExecution>
            </handler>
        </handlerchain>
    </lmtpserver>
</lmtpservers>