You already have a QuestSoftware section in your web.config file (see below the text in Italic font), and I just added the line in bold.
This is how your section would look like:
<QuestSoftware>
<MailSettings OutboundSmtpServer="smtp.mailposte.ca" />
<ComplexCategory DefaultBlankCategoryName="(Not Categorized)" />
<General HideQuestRibbon="True" />
</QuestSoftware>