Version 4.01
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 1. When sender verification fails in an ACL, the details of the failure are
    given as additional output lines before the 550 response to the relevant
    SMTP command (RCPT or DATA). For example, if sender callout is in use, you
    might see:

      MAIL FROM:<xyz@abc.example>
      250 OK
      RCPT TO:<pqr@def.example>
      550-Verification failed for <xyz@abc.example>
      550-Called:   192.168.34.43
      550-Sent:     RCPT TO:<xyz@abc.example>
      550-Response: 550 Unknown local part xyz in <xyz@abc.example>
      550 Sender verification failed

    If more than one RCPT command fails, the details are given only for the
    first of them. However, not everybody wants to send out this much
    information, it seems. You can now suppress this by adding "/no_details"
    to the ACL statement that requests sender verification. For example:

      verify = sender/no_details

 2. There is a new command line option -oP which allows the pid file path to
    be specified on the command line. The rules for deciding whether an Exim
    daemon should write a pid file have been changed and are now as follows:

    . A pid file is not written unless the -bd option is used (that is, daemons
      created with -q that don't do SMTP listening are esoteric beasts that
      don't count).

    . A pid file is not written when -oX is used to override the SMTP port or
      the interfaces, unless -oP is used to specify a path explicitly.