When the autoLogin attribute is set to true on certain [MM_..._Link] SmartTags*, a login token is created that allows the customer to be automatically logged in when they click the link. The auto login link sent to the customer will only be valid for a specific period of time. The default lifespan is 15 days but this value can be changed on General Settings > Other Settings > Login Token Settings.
If multiple auto login links are requested by the same user within a 24-hour period, they will all use the same login token.
* See these SmartTag articles for more information on usage: