Each file link has a file type icon. However, these icons are lost when an email is sent to an external mail system, such as Gmail or Hotmail.
After inserting file links in an email, if you send the email to a user that uses a mail system other than Connections Mail, the user receiving the email may see a broken icon or nothing where there should be a file type icon.
File type icons are implemented by image data URI. Some mail systems filter out image data URIs.
Resolving the problem
There is currently no work around. This issue has been reported to IBM Connections Mail development.