By default, users receive regular emails with new posts and the like from sites they're a member of, based on the permissions their account has for that site.  If you would rather not receive this email, you can deactivate it like so:

• Click your Username at the top right of the Guild Launch site you're logged into.
• Click the Communications tab.
• Click Email Notifications.
• Toggle the Guild Activity Update notification from Yes to No for your guild.
• Click Save Site Specific Settings.