When creating tasks in Outlook (MAPI), it's possible to attach various files, as needed, to those tasks. Spreadsheets, text files, images, etc. can all be added. In addition, many times, when a task is created, it is assigned to someone else within your organization.
Most of the time, this isn't an issue. A long as the person who was assigned the task is also using Outlook, these attachments can be seen and interacted with. However, if the person assigned the task uses webmail, the attachments are lost.
It's important to note that this is NOT a SmarterMail issue. It's because of the way Outlook encodes the attachments. Microsoft uses a proprietary format that can only be read by Outlook. The attachments are not viewable or usable in any other client. So if someone is using a different email client, or webmail, the attachments will need to be emailed separately or the user assigned the task will need to use Outlook.