Setting the Defer E-Mail (Budget delivery) option

Configure->LocalConfig->DeferEMail

You can set whether outgoing e-mail is to be send immediately, or deferred until the next mail collection takes place. On a dial-up connection, deferring email delivery can reduce telephony charges appreciably, but also delays delivery of the e-mail.  If the immediate delivery option is chosen, the Server will dial up every time any user sends an e-mail to an outside recipient.  Deferred delivery does not apply to internal e-mail, which is always delivered immediately.

The default setting for this option is immediate delivery, or "External e-mail sent immediately".