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, and DIGEST-MD5 mechanisms (RFC 2592 and RFC 2831).

To use SMTP authentication you'll need to set the `mail.smtp.auth` property (see below) and 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`.

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. JavaMail does not currently provide direct support for these new MIME types, but you can process them as any other "multipart" or "message" content, using `MimeMultipart` and `MimeMessage` objects.

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!!!

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.

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. Default is infinite timeout.
mail.smtp.timeout | int | Socket I/O timeout value in milliseconds. 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.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.realm | String | The realm to use with DIGEST-MD5 authentication.
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.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.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.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.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.

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.

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.