### 2.4 Program Mailboxes ¶

Program mailboxes support only append operation. Appending a message is performed by invoking the specified program and passing the message to its standard input stream.

A ‘`sendmail`’ mailbox is identified by the following URL:

    sendmail[://path]

The messages are sent by invoking `sendmail` binary with the `-oi -t` options. If the message being appended has the ‘`From:`’ header, its value is passed to `sendmail` using the `-f` option.

The default path to the sendmail binary is system-dependent. The path part can be used to specify it explicitly.

The ‘`prog`’ mailbox URL is:

    prog://pathname[?query]

Messages are appended by invoking the program pathname with the arguments supplied by query. The latter is a list of words delimited by ‘`&`’ characters.

Arguments can contain the following variables (see Configuration Variables):

sender ¶

  Expands to the sender email address.

rcpt ¶

  Expands to comma-separated list of email addresses obtained from ‘`To:`’, ‘`Cc:`’ and ‘`Bcc:`’ headers of the message.