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-mailcontrols whether a simple off line mail sender is active. This variable is a boolean, and defaults to
nil(disabled). If this is non-
nil, mail is not sent immediately but rather queued in the directory
smtpmail-queue-dirand can be later sent manually by invoking
smtpmail-send-queued-mail(typically when you connect to the internet).
smtpmail-queue-dirspecifies the name of the directory to hold queued messages. It defaults to ~/Mail/queued-mail/.
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.