Outlook client giving error when replying or forwarding email chain, with or without attachment and getting an error: “This is not a valid file name”. The issue could be local outlook setting, plugin as well links, or images broken. The best way to check via Web outlook is to test your issue, if the web works then look at the settings of outlook. Here are some options that may help fix your issues.
Look at the body of the email:
Look at all links and empty areas of the body to see if there are any hidden links, Like the example below
Once removed any broken links, your issue should be fixed
Also, you can try converting the HTML to Plain Text, which will remove all formatting and links
Check outlook in Safe mode:
Click Start > Run.
Type Outlook /safe, and choose OK
Take a look at the Plugin of outlook:
You can get to it by going to File>Options>Add-ins
Just uncheck to disable whichever you don’t use or causing the issue
Getting errors when trying to open an attachment from Outlook something like “cannot save the attachment. Cannot create file: FileName.pdf. Right-click the folder you want to create the file in, and then click Properties on the shortcut menu to check your permissions for the folder.” This may be due to permission or a corrupted temp directory. Here is how to fix it, one thing you could try without doing anything is to restart the computer, if that does not fix try the following options.
Option 1: rename temp folder
The temp folder of outlook is located at the following location: “YourUserName” which would be your own user name, anything after Content.Outlook\ would be randomly created folder name by an Outlook
Make sure your Outlook is closed, then rename to old or anything you want or simply delete it. Then re-open the outlook, it should recreate the temp folder and your attachment should be fixed
Then change the OutlookSecureTempFolder location to somewhere you have access. Remember this is the default location, if you do change the custom, and when an update applies it may revert. When you open the outlook it should work now, you should see new random folder after your default location.