To Add and remove file types attachments with outlook 2010:

1.Open registry (click “start” <Run < type “regedit”  <click “Run”.
2.HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
3.To create ADD list – type a string value named Level1Add < set as value all attachment list you wish to add with separated comma (.html;.xls)
4.To create Remove list – type a string value named Level1Remove < set as value all attachment list you wish to remove with separated comma (same as step 3).
5.Reset computer.