How to use the global exclusions list in Backup Exec
Follow these steps to create the global exclusion list:
1. Open Veritas Backup Exec.
2. From Home button, click 'Configuration and Settings' > 'Job Defaults' > 'Exclude Selections' as shown in below figure.

3. Select the Insert tab.

4. Then add the extension to the 'Name' field.
The following example shows all the files that have "*.txt" as an extension to be excluded.

5. Click OK to close
For more details refer to Backup Exec admin guide --> Excluding files from backups
Folder or Share Exclusion:

How to use the global exclusions list to create a global exclusion for a specific file extension in Backup Exec.