Mode Z compression compresses files on-the-fly for file transfers from the local computer to the remote computer and remote to local computer, saving bandwidth and improving transfer time. You must configure MODE Z to take advantage of this feature. If MODE Z option is enabled, then all the file types in the Mode Z list are compressed when transfer of files between the computers take place.
From the Deva xFTP menu, select Tools > Options The GlobalOptions dialog box opens.

Select the Apply MODE Z compression check box to enable the compression of files. Mode Z compression is applied to all file types in the following list.
Click Apply.
Enter the extension of the file in the text field and click Add.
Select the extension of the file from the Mode Z list and click Remove.
Note:
Only those files that are added to the Mode Z list are compressed.