Sometimes it may happen that because of unforeseen circumstances it may be not possible to sent email message (1). This may be caused by for example temporary smtp server malfunction. When you try to send email via i..e post-function template of Email Task and it is not possible.
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As you can see, each failed message is highlighted in light reddish color. Possibility to re-send message is included. Option for doing so is available at at the bottom of each failed to be be send message (2).