What happens when an email from webform fails to deliver? If webform attempts to send an email but cannot connect to the smtp server, what happens to the email? Does it get dropped on the floor? Does it throw an error in a log? Does it try to resend later? Does it mark it somewhere as unsent?
It throws an error and drop it on floor like below:

Warning: mail() [function.mail]: Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set() in DefaultMailSystem-&gt;mail() (line 76 of \modules\system\system.mail.inc).
Unable to send e-mail. Contact the site administrator if the problem persists.
Warning: mail() [function.mail]: Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set() in DefaultMailSystem-&gt;mail() (line 76 of \modules\system\system.mail.inc).
Unable to send e-mail. Contact the site administrator if the problem persists.