Lately, all my attachments are being received as gz-files. For instance a Word document comes in as a .docx.gz file instead of a .docx files.
How can I can I receive my emails normally again with their original extension?
A gz-file is a Gzip Compressed Archive file. It can be opened by many popular uncompressing tools like WinRAR, WinZIP and 7UP. Normally, the sender could compress a file so the file to be send would be smaller. However, when you receive all your attachments from anyone as a gz-file as well, it could mean you either have something installed that does this or there is something going on at mail server level.
There are several attachment compression add-ins which can zip your attachment files so they will take up less space in your mailbox. If you have something like that installed, it could be that you have set it to compress incoming messages as well and use the gz-file format as the default.
A good way to test this is to start Outlook in Safe Mode and then send yourself a message with an attachment and see how it comes in now. If it comes in normally, you’ll have to check which add-ins you have installed.
Mail Server configuration
If the above doesn’t solve it, it could be that there is a mail server misconfiguration. Some mail servers (especially Linux based ones) can store everything in a compressed gz-format but will eventually serve the uncompressed file when a mail client downloads the mail from the server.
If you have an additional account on that server (or you know somebody that has) and you download the emails from that account with a different computer and you still have the issue, you can be quite sure that the issue is at server level and not a local issue on your computer.