Notification: Your message was sent but a copy was not placed in your sent folder (Sent) due to network or file access errors. You can retry or save the message locally to Local Folders/Sent-[email]@earthlink.net. What is happening?

The message is real. Network problems happen. I get that message myself on occasion. If it happens excessively, I suggest contacting earthlink.

I have this problem too. It seems from various sites this is a widespread and long lived problem. Surely it deserves attention.

I can find no network issue. I have a fibre connection (940/100) and all tests show good connnection. The email providers servers are showing no faults.

I have seen a post suggesting on Stack Exchange suggesting its the inability of the hard disk to service multiple requests to read/write large mailbox files.

My mail box is around 15GB. My email provider has confirmed this is not an issue - they allow mailbox sizes of up to 50GB, wit suitably capable servers. Also, my disk is a Samsung 970 EVO Plus Series 1TB M.2 2280 M-Key PCIe NVMe SSD Drive - I would think this would be fast enough

I have this problem too.

I'm having the same problem. I need the email on the server and can access them normally from one PC. The issue is with the email a second PC on the same site. The permissions should be the same and the same direct fibre access to the internet. Everything worked fine until about a fortnight ago. Any help or solution to this would be much appreciated.