E-Mail Services consists of a set of products and services that handles e-mails within Office 365:
1) 'Incoming E-Mail': Allows you to transfer e-mails from any mailbox to any list or document libary in SharePoint Online. This service brings e-mail enabled lists and libraries to Office 365.
Incoming E-Mail is available as a free, fully featured plan with 100 e-mails per month included. If you need more you can choose from a series of plans. For more details please visit http://www.office-cloud-services.com/en/pricing
2) 'E-Mail Filing': Allows to file e-mails with metadata from your Outlook 2013 or Outlook Web Access to any document library in SharePoint Online. (Preview coming up soon)
E-Mail Services does not support Internet Explorer 8.0.