The file extension MAILHOST is exclusive to Microsoft and is used with MSN email applications. The file is automatically installed on your device when you download the MSN Explorer email application. MAILHOST files are a necessary component for running MSN email applications and will automatically update whenever you change your preferences in the MSN email client.
MAILHOST files contain data which is required for sending and receiving email messages in addition to storing preferences and email settings. If the file is accidentally deleted or becomes corrupt, the MSN email client will display an error message which prevents you from opening and viewing email messages.
This error is known to be quite common with the MSN email client and can easily be fixed by clicking on Start on the main toolbar in Windows and choosing Run from the pop-up menu. If you run Windows 7, you should use the Start Search box. When the command prompt appears, enter the following information: regsvr32 c:\progra~1\msn\msncorefiles\mailui.dll and then press the Enter key. This will repair the MAILHOST file and place your MSN email client back in proper working order.
How to Open MAILHOST Files
MAILHOST files can appear with the name MSN#.mailhost, which is basically the same file. Since MAILHOST files are proprietary Microsoft files and created with the MSN Explorer email client, using the MSN email application is the most obvious option for opening and viewing these files.
MAILHOST files are text-based. This makes it possible to open and view the contents using a text editor. If you use Windows, you can open and view MAILHOST files in Notepad or WordPad. Simply right click on the file and choose Open With from the drop-down menu. Select the text editor you want to use from the list or click on Browse if the program is not listed on the submenu.
If you use Mac OS X, you can try to open MAILHOST files using TextEdit. For the Linux operating system you can view the contents of a MAILHOST file using the open source gedit text editing program.
If you have trouble opening a MAILHOST file, you can use the method described earlier for repairing the file by re-registering it in your PC. You can also choose to download a program such as FileCure which is capable of opening unsupported file types and files that have become damaged or corrupt.
As a general rule, MAILHOST files cannot be converted to another format since they are exclusive to the MSN Explorer email client and store the email server preferences for using the program.