If you connect to the internet via a dialup connection, or for some other reason don’t have permanent internet connection, sending mail will fail when you are not connected. The SMTP library implements queued delivery, and the following variable control its behavior.
smtpmail-queue-mail controls whether a simple
off line mail sender is active. This variable is a boolean, and
nil (disabled). If this is non-
nil, mail is
not sent immediately but rather queued in the directory
smtpmail-queue-dir and can be later sent manually by invoking
smtpmail-send-queued-mail (typically when you connect to the
smtpmail-queue-dir specifies the name of the
directory to hold queued messages. It defaults to
smtpmail-send-queued-mail can be used to send
any queued mail when
smtpmail-queue-mail is enabled. It is
typically invoked interactively with M-x
smtpmail-send-queued-mail RET when you are connected to the internet.