LETTER File Extension

What is LETTER file?

Full format name of files that use LETTER extension is Undeliverable Mail Format. LETTER file format is compatible with software that can be installed on Linux, Mac OS, Windows system platform. Files with LETTER extension are categorized as Misc Files files. The Misc Files subset comprises 6033 various file formats. The most popular program for handling LETTER files is Sendmail, but users can choose among 2 different programs that support this file format.

Programs which support LETTER file extension

The following list contains programs grouped by 3 operating systems that support LETTER files. Files with LETTER extension, just like any other file formats, can be found on any operating system. The files in question may be transferred to other devices, be it mobile or stationary, yet not all systems may be capable of properly handling such files.

How to open file with LETTER extension?

There can be multiple causes why you have problems with opening LETTER files on given system. Fortunately, most common problems with LETTER files can be solved without in-depth IT knowledge, and most importantly, in a matter of minutes. The following is a list of guidelines that will help you identify and solve file-related problems.

Step 1. Download and install Sendmail

The main and most frequent cause precluding users form opening LETTER files is that no program that can handle LETTER files is installed on user’s system. The solution is straightforward, just download and install Sendmail. The full list of programs grouped by operating systems can be found above. The safest method of downloading Sendmail installed is by going to developer’s website () and downloading the software using provided links.

Step 2. Verify the you have the latest version of Sendmail

If you already have Sendmail installed on your systems and LETTER files are still not opened properly, check if you have the latest version of the software. Sometimes software developers introduce new formats in place of that already supports along with newer versions of their applications. The reason that Sendmail cannot handle files with LETTER may be that the software is outdated. The most recent version of Sendmail is backward compatible and can handle file formats supported by older versions of the software.

Step 3. Associate Undeliverable Mail Format files with Sendmail

After installing Sendmail (the most recent version) make sure that it is set as the default application to open LETTER files. The method is quite simple and varies little across operating systems.

Selecting the first-choice application in Windows

• Choose the Open with entry from the file menu accessed by right-mouse clicking on the LETTER file
• Select Choose another app → More apps
• The last step is to select Look for another app on this PC option supply the directory path to the folder where Sendmail is installed. Now all that is left is to confirm your choice by selecting Always use this app to open LETTER files and clicking OK.

Selecting the first-choice application in Mac OS

• From the drop-down menu, accessed by clicking the file with LETTER extension, select Information
• Find the Open with option – click the title if its hidden
• Select the appropriate software and save your settings by clicking Change all
• If you followed the previous steps a message should appear: This change will be applied to all files with LETTER extension. Next, click the Continue button to finalize the process.

Step 4. Check the LETTER for errors

If you followed the instructions form the previous steps yet the issue is still not solved, you should verify the LETTER file in question. Being unable to access the file can be related to various issues.

1. Verify that the LETTER in question is not infected with a computer virus

Should it happed that the LETTER is infected with a virus, this may be that cause that prevents you from accessing it. Immediately scan the file using an antivirus tool or scan the whole system to ensure the whole system is safe. If the scanner detected that the LETTER file is unsafe, proceed as instructed by the antivirus program to neutralize the threat.

2. Check whether the file is corrupted or damaged

If you obtained the problematic LETTER file from a third party, ask them to supply you with another copy. During the copy process of the file errors may occurred rendering the file incomplete or corrupted. This could be the source of encountered problems with the file. It could happen the the download process of file with LETTER extension was interrupted and the file data is defective. Download the file again from the same source.

3. Check if the user that you are logged as has administrative privileges.

Some files require elevated access rights to open them. Log out of your current account and log in to an account with sufficient access privileges. Then open the Undeliverable Mail Format file.

4. Check whether your system can handle Sendmail

If the systems has insufficient resources to open LETTER files, try closing all currently running applications and try again.

5. Check if you have the latest updates to the operating system and drivers

Regularly updated system, drivers, and programs keep your computer secure. This may also prevent problems with Undeliverable Mail Format files. It may be the case that the LETTER files work properly with updated software that addresses some system bugs.

Do you want to help?

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