Windows Live Hotmail allows users to view attachments within a Web browser or save them to the system's hard drive. If Hotmail can't open an attachment, the problem lies with an incompatible file format or Hotmail's automatic blocking service. You may need new software for opening unfamiliar formats, while blocked files are permanently inaccessible from within Hotmail. Accessing these files requires action by the sender or forwarding the file to a different e-mail client.
Incompatible File Format
Occasionally a sender may attach a file that simply doesn't work with any software you have installed on the system. Attempting to open the attachment will result in a "Windows cannot open this file" message or similar error display. Many programs use very specific file formats that don't operate with most other software, such as Photoshop's PSD image files or Microsoft PowerPoint's PPT files. Ask the sender to convert the file to a more widely compatible format, or install the appropriate software on the system to open the attachment.
Hotmail blocks attachments it believes may contain unsafe or otherwise malicious code. This includes any and all executable file types, including MSI, EXE, HTML, STC and COM files, along with many others. Attachments blocked in this way result in a "Windows Live Hotmail has blocked some attachments" message when viewing the email. While this service does block many real threats to system security, Hotmail may occasionally deny access to an item from a trusted sender. Unfortunately, these files become permanently inaccessible once blocked by Hotmail, and accessing them requires using a workaround outside the Hotmail application. Only attempt to access attachments you trust as safe.
While Hotmail cannot open blocked attachments, it allows users to forward the message with the blocked file still attached. Send the file to a different e-mail client, and open the attachment using that account instead. Note other clients may have different security measures, but some will still block access to executable files and other potentially harmful data.
Ask the sender to package the attachment into a ZIP, RAR or other compressed file format before attaching. Hotmail will not block any file type located inside a compressed archive. Both Windows and OS X can create compressed ZIP files, and free utilities such as Zipeg and 7-Zip can create many other types of archives as well. Some e-mail clients, such as Gmail, will not allow users to send some file formats, even when packaged into an archive file.