Last night I did an upgrade of my Arch Linux system. Today I opened my e-mail to find all my e-mail missing except my inbox…!
The e-mail was still on in my ~/Mail folder, but not in KMail. I was able to find it again by going into “Settings” > “Configure KMail”, and to the “Accounts” section.
Here, under “Receiving”, I had “Gmail” with all three “Retrieval Options” checked, but “Local Folders” had only “Include in Manual Mail Check” and “KMail Folders” had nothing checked. I checked “Include in Manual Mail Check” on the latter, and “Check Mail on Startup” on both, then closed and re-opened KMail. All my missing e-mails are back!
I’m sure I could have just clicked on “Check Mail” rather than restarting KMail, and I might want to uncheck some of those options I checked (for better performance), but for now I’m glad to just have my missing e-mails accessible again.