I have an old listserver that uses Mercury Mail. When I say old I mean prior to 2011 and running on Windows 2003 Server. I will be upgrading this to a newer version of listserver but in the meantime I need to gain back more disk space. My question is, can I safely delete .CNM files? There are several hundred thousand. They all appear to be log files of delivery failures.

CNM files are message files, each contains one email message. If the server has been unattended for a while a lot of junk may have accumulated, but if you remove all there won't be any messages left other than those moved to IMAP folders.

Thank you Rolf. All this appears to be are email errors. This is a list server, so those messages don't appear to show up here from what I can see.