An SMTP protocol provider for the JavaMail API that provides access to an SMTP server. Refer to RFC 821 for more information.

When sending a message, detailed information on each address that fails is available in an {@link com.sun.mail.smtp.SMTPAddressFailedException SMTPAddressFailedException} chained off the top level {@link javax.mail.SendFailedException SendFailedException} that is thrown. In addition, if the `mail.smtp.reportsuccess` property is set, an {@link com.sun.mail.smtp.SMTPAddressSucceededException SMTPAddressSucceededException} will be included in the list for each address that is successful. Note that this will cause a top level {@link javax.mail.SendFailedException SendFailedException} to be thrown even though the send was successful.

The SMTP provider also supports ESMTP (RFC 1651). It can optionally use SMTP Authentication (RFC 2554) using the LOGIN, PLAIN, DIGEST-MD5, and NTLM mechanisms (RFC 2595 and RFC 2831).

To use SMTP authentication you'll need to set the `mail.smtp.auth` property (see below) or provide the SMTP Transport with a username and password when connecting to the SMTP server. You can do this using one of the following approaches:

- Provide an Authenticator object when creating your mail Session and provide the username and password information during the Authenticator callback.

  Note that the `mail.smtp.user` property can be set to provide a default username for the callback, but the password will still need to be supplied explicitly.

  This approach allows you to use the static Transport `send` method to send messages.

- Call the Transport `connect` method explicitly with username and password arguments.

  This approach requires you to explicitly manage a Transport object and use the Transport `sendMessage` method to send the message. The transport.java demo program demonstrates how to manage a Transport object. The following is roughly equivalent to the static Transport `send` method, but supplies the needed username and password:

  >     Transport tr = session.getTransport("smtp");
  >     tr.connect(smtphost, username, password);
  >     msg.saveChanges();	// don't forget this
  >     tr.sendMessage(msg, msg.getAllRecipients());
  >     tr.close();

When using DIGEST-MD5 authentication, you'll also need to supply an appropriate realm; your mail server administrator can supply this information. You can set this using the `mail.smtp.sasl.realm` property, or the `setSASLRealm` method on `SMTPTransport`.

The SMTP protocol provider can use SASL (RFC 2222) authentication mechanisms on systems that support the `javax.security.sasl` APIs, such as J2SE 5.0. In addition to the SASL mechanisms that are built into the SASL implementation, users can also provide additional SASL mechanisms of their own design to support custom authentication schemes. See the Java SASL API Programming and Deployment Guide for details. Note that the current implementation doesn't support SASL mechanisms that provide their own integrity or confidentiality layer.

Support for OAuth 2.0 authentication via the XOAUTH2 authentication mechanism is provided either through the SASL support described above or as a built-in authentication mechanism in the SMTP provider. The OAuth 2.0 Access Token should be passed as the password for this mechanism. See OAuth2 Support for details.

SMTP can also optionally request Delivery Status Notifications (RFC 1891). The delivery status will typically be reported using a "multipart/report" (RFC 1892) message type with a "message/delivery-status" (RFC 1894) part. You can use the classes in the {@link com.sun.mail.dsn} package to handle these MIME types. Note that you'll need to include `dsn.jar` in your CLASSPATH as this support is not included in `mail.jar`.

See below for the properties to enable these features.

Note also that THERE IS NOT SUFFICIENT DOCUMENTATION HERE TO USE THESE FEATURES!!! You will need to read the appropriate RFCs mentioned above to understand what these features do and how to use them. Don't just start setting properties and then complain to us when it doesn't work like you expect it to work. READ THE RFCs FIRST!!!

#### Properties

The SMTP protocol provider supports the following properties, which may be set in the JavaMail `Session` object. The properties are always set as strings; the Type column describes how the string is interpreted. For example, use

    	props.put("mail.smtp.port", "888");

to set the `mail.smtp.port` property, which is of type int.

Note that if you're using the "smtps" protocol to access SMTP over SSL, all the properties would be named "mail.smtps.*".

Name | Type | Description
--- | --- | ---
mail.smtp.user | String | Default user name for SMTP.
mail.smtp.host | String | The SMTP server to connect to.
mail.smtp.port | int | The SMTP server port to connect to, if the connect() method doesn't explicitly specify one. Defaults to 25.
mail.smtp.connectiontimeout | int | Socket connection timeout value in milliseconds. This timeout is implemented by java.net.Socket. Default is infinite timeout.
mail.smtp.timeout | int | Socket read timeout value in milliseconds. This timeout is implemented by java.net.Socket. Default is infinite timeout.
mail.smtp.writetimeout | int | Socket write timeout value in milliseconds. This timeout is implemented by using a java.util.concurrent.ScheduledExecutorService per connection that schedules a thread to close the socket if the timeout expires. Thus, the overhead of using this timeout is one thread per connection. Default is infinite timeout.
mail.smtp.from | String | Email address to use for SMTP MAIL command. This sets the envelope return address. Defaults to msg.getFrom() or InternetAddress.getLocalAddress(). NOTE: mail.smtp.user was previously used for this.
mail.smtp.localhost | String | Local host name used in the SMTP HELO or EHLO command. Defaults to `InetAddress.getLocalHost().getHostName()`. Should not normally need to be set if your JDK and your name service are configured properly.
mail.smtp.localaddress | String | Local address (host name) to bind to when creating the SMTP socket. Defaults to the address picked by the Socket class. Should not normally need to be set, but useful with multi-homed hosts where it's important to pick a particular local address to bind to.
mail.smtp.localport | int | Local port number to bind to when creating the SMTP socket. Defaults to the port number picked by the Socket class.
mail.smtp.ehlo | boolean | If false, do not attempt to sign on with the EHLO command. Defaults to true. Normally failure of the EHLO command will fallback to the HELO command; this property exists only for servers that don't fail EHLO properly or don't implement EHLO properly.
mail.smtp.auth | boolean | If true, attempt to authenticate the user using the AUTH command. Defaults to false.
mail.smtp.auth.mechanisms | String | If set, lists the authentication mechanisms to consider, and the order in which to consider them. Only mechanisms supported by the server and supported by the current implementation will be used. The default is `"LOGIN PLAIN DIGEST-MD5 NTLM"`, which includes all the authentication mechanisms supported by the current implementation except XOAUTH2.
mail.smtp.auth.login.disable | boolean | If true, prevents use of the `AUTH LOGIN` command. Default is false.
mail.smtp.auth.plain.disable | boolean | If true, prevents use of the `AUTH PLAIN` command. Default is false.
mail.smtp.auth.digest-md5.disable | boolean | If true, prevents use of the `AUTH DIGEST-MD5` command. Default is false.
mail.smtp.auth.ntlm.disable | boolean | If true, prevents use of the `AUTH NTLM` command. Default is false.
mail.smtp.auth.ntlm.domain | String | The NTLM authentication domain.
mail.smtp.auth.ntlm.flags | int | NTLM protocol-specific flags. See http://curl.haxx.se/rfc/ntlm.html#theNtlmFlags for details.
mail.smtp.auth.xoauth2.disable | boolean | If true, prevents use of the `AUTHENTICATE XOAUTH2` command. Because the OAuth 2.0 protocol requires a special access token instead of a password, this mechanism is disabled by default. Enable it by explicitly setting this property to "false" or by setting the "mail.smtp.auth.mechanisms" property to "XOAUTH2".
mail.smtp.submitter | String | The submitter to use in the AUTH tag in the MAIL FROM command. Typically used by a mail relay to pass along information about the original submitter of the message. See also the {@link com.sun.mail.smtp.SMTPMessage#setSubmitter setSubmitter} method of {@link com.sun.mail.smtp.SMTPMessage SMTPMessage}. Mail clients typically do not use this.
mail.smtp.dsn.notify | String | The NOTIFY option to the RCPT command. Either NEVER, or some combination of SUCCESS, FAILURE, and DELAY (separated by commas).
mail.smtp.dsn.ret | String | The RET option to the MAIL command. Either FULL or HDRS.
mail.smtp.allow8bitmime | boolean | If set to true, and the server supports the 8BITMIME extension, text parts of messages that use the "quoted-printable" or "base64" encodings are converted to use "8bit" encoding if they follow the RFC2045 rules for 8bit text.
mail.smtp.sendpartial | boolean | If set to true, and a message has some valid and some invalid addresses, send the message anyway, reporting the partial failure with a SendFailedException. If set to false (the default), the message is not sent to any of the recipients if there is an invalid recipient address.
mail.smtp.sasl.enable | boolean | If set to true, attempt to use the javax.security.sasl package to choose an authentication mechanism for login. Defaults to false.
mail.smtp.sasl.mechanisms | String | A space or comma separated list of SASL mechanism names to try to use.
mail.smtp.sasl.authorizationid | String | The authorization ID to use in the SASL authentication. If not set, the authentication ID (user name) is used.
mail.smtp.sasl.realm | String | The realm to use with DIGEST-MD5 authentication.
mail.smtp.sasl.usecanonicalhostname | boolean | If set to true, the canonical host name returned by {@link java.net.InetAddress#getCanonicalHostName InetAddress.getCanonicalHostName} is passed to the SASL mechanism, instead of the host name used to connect. Defaults to false.
mail.smtp.quitwait | boolean | If set to false, the QUIT command is sent and the connection is immediately closed. If set to true (the default), causes the transport to wait for the response to the QUIT command.
mail.smtp.reportsuccess | boolean | If set to true, causes the transport to include an {@link com.sun.mail.smtp.SMTPAddressSucceededException SMTPAddressSucceededException} for each address that is successful. Note also that this will cause a {@link javax.mail.SendFailedException SendFailedException} to be thrown from the {@link com.sun.mail.smtp.SMTPTransport#sendMessage sendMessage} method of {@link com.sun.mail.smtp.SMTPTransport SMTPTransport} even if all addresses were correct and the message was sent successfully.
mail.smtp.socketFactory | SocketFactory | If set to a class that implements the `javax.net.SocketFactory` interface, this class will be used to create SMTP sockets. Note that this is an instance of a class, not a name, and must be set using the `put` method, not the `setProperty` method.
mail.smtp.socketFactory.class | String | If set, specifies the name of a class that implements the `javax.net.SocketFactory` interface. This class will be used to create SMTP sockets.
mail.smtp.socketFactory.fallback | boolean | If set to true, failure to create a socket using the specified socket factory class will cause the socket to be created using the `java.net.Socket` class. Defaults to true.
mail.smtp.socketFactory.port | int | Specifies the port to connect to when using the specified socket factory. If not set, the default port will be used.
mail.smtp.ssl.enable | boolean | If set to true, use SSL to connect and use the SSL port by default. Defaults to false for the "smtp" protocol and true for the "smtps" protocol.
mail.smtp.ssl.checkserveridentity | boolean | If set to true, check the server identity as specified by RFC 2595. These additional checks based on the content of the server's certificate are intended to prevent man-in-the-middle attacks. Defaults to false.
mail.smtp.ssl.trust | String | If set, and a socket factory hasn't been specified, enables use of a {@link com.sun.mail.util.MailSSLSocketFactory MailSSLSocketFactory}. If set to "*", all hosts are trusted. If set to a whitespace separated list of hosts, those hosts are trusted. Otherwise, trust depends on the certificate the server presents.
mail.smtp.ssl.socketFactory | SSLSocketFactory | If set to a class that extends the `javax.net.ssl.SSLSocketFactory` class, this class will be used to create SMTP SSL sockets. Note that this is an instance of a class, not a name, and must be set using the `put` method, not the `setProperty` method.
mail.smtp.ssl.socketFactory.class | String | If set, specifies the name of a class that extends the `javax.net.ssl.SSLSocketFactory` class. This class will be used to create SMTP SSL sockets.
mail.smtp.ssl.socketFactory.port | int | Specifies the port to connect to when using the specified socket factory. If not set, the default port will be used.
mail.smtp.ssl.protocols | string | Specifies the SSL protocols that will be enabled for SSL connections. The property value is a whitespace separated list of tokens acceptable to the `javax.net.ssl.SSLSocket.setEnabledProtocols` method.
mail.smtp.ssl.ciphersuites | string | Specifies the SSL cipher suites that will be enabled for SSL connections. The property value is a whitespace separated list of tokens acceptable to the `javax.net.ssl.SSLSocket.setEnabledCipherSuites` method.
mail.smtp.starttls.enable | boolean | If true, enables the use of the `STARTTLS` command (if supported by the server) to switch the connection to a TLS-protected connection before issuing any login commands. Note that an appropriate trust store must configured so that the client will trust the server's certificate. Defaults to false.
mail.smtp.starttls.required | boolean | If true, requires the use of the `STARTTLS` command. If the server doesn't support the STARTTLS command, or the command fails, the connect method will fail. Defaults to false.
mail.smtp.socks.host | string | Specifies the host name of a SOCKS5 proxy server that will be used for connections to the mail server. (Note that this only works on JDK 1.5 or newer.)
mail.smtp.socks.port | string | Specifies the port number for the SOCKS5 proxy server. This should only need to be used if the proxy server is not using the standard port number of 1080.
mail.smtp.mailextension | String | Extension string to append to the MAIL command. The extension string can be used to specify standard SMTP service extensions as well as vendor-specific extensions. Typically the application should use the {@link com.sun.mail.smtp.SMTPTransport SMTPTransport} method {@link com.sun.mail.smtp.SMTPTransport#supportsExtension supportsExtension} to verify that the server supports the desired service extension. See RFC 1869 and other RFCs that define specific extensions.
mail.smtp.userset | boolean | If set to true, use the RSET command instead of the NOOP command in the {@link javax.mail.Transport#isConnected isConnected} method. In some cases sendmail will respond slowly after many NOOP commands; use of RSET avoids this sendmail issue. Defaults to false.
mail.smtp.noop.strict | boolean | If set to true (the default), insist on a 250 response code from the NOOP command to indicate success. The NOOP command is used by the {@link javax.mail.Transport#isConnected isConnected} method to determine if the connection is still alive. Some older servers return the wrong response code on success, some servers don't implement the NOOP command at all and so always return a failure code. Set this property to false to handle servers that are broken in this way. Normally, when a server times out a connection, it will send a 421 response code, which the client will see as the response to the next command it issues. Some servers send the wrong failure response code when timing out a connection. Do not set this property to false when dealing with servers that are broken in this way.

In general, applications should not need to use the classes in this package directly. Instead, they should use the APIs defined by `javax.mail` package (and subpackages). Applications should never construct instances of `SMTPTransport` directly. Instead, they should use the `Session` method `getTransport` to acquire an appropriate `Transport` object.

In addition to printing debugging output as controlled by the {@link javax.mail.Session Session} configuration, the com.sun.mail.smtp provider logs the same information using {@link java.util.logging.Logger} as described in the following table:

Logger Name | Logging Level | Purpose
--- | --- | ---
com.sun.mail.smtp | CONFIG | Configuration of the SMTPTransport
com.sun.mail.smtp | FINE | General debugging output
com.sun.mail.smtp.protocol | FINEST | Complete protocol trace

WARNING: The APIs unique to this package should be considered EXPERIMENTAL. They may be changed in the future in ways that are incompatible with applications using the current APIs.