CASE 01 / VISIBLE TITLE, EMPTY MESSAGE
It loads online, then disappears offline.
First establish whether the full message body was downloaded. Seeing a sender and subject is not proof that every attachment is stored locally. With a non-sensitive test message, open its body and attachment online, then disconnect and try again. Record the two outcomes separately.
Mozilla’s IMAP synchronisation guide explains the distinction between headers and synchronised content. Inspect the relevant desktop account’s offline settings rather than assuming every folder has the same policy. This observation does not measure delivery speed or prove that a provider deleted anything.
Worked observation: “Tuesday’s test email opens offline; its 40 KB attachment does not.” That narrows the next check to attachment availability. “My email is broken” does not.
CASE 02 / TEN YEARS ON THE DESKTOP, ONE YEAR ONLINE
The new device can’t fetch a local archive.
Find the old message in the desktop folder tree and compare it with webmail. If it exists only under Local Folders or in a POP download, another client cannot retrieve it merely by signing into the same server account. Confirm the account type in its settings; do not infer it from a familiar address.
Make a separate verified backup before reorganising historical mail. If you intend to move local mail into an IMAP account, check provider storage and test a small copied set while keeping the originals. Mozilla’s POP-to-IMAP guide covers the account change; a protocol switch is a separate job from installing a phone app.
Worked observation: Nina finds a 2020 invoice in “Local Folders / Old orders”, but not in webmail. Her next task is preserving and deliberately transferring that archive, not repeatedly refreshing the phone inbox.
CASE 03 / TWO NAMES, MAYBE ONE COPY
Folder views don’t always describe storage.
Compare a particular message’s date, sender, subject and, where available, Message-ID. A search result, combined inbox or provider label can show the same message in more than one view. Two visible rows alone do not establish two separately stored copies.
Open the corresponding folder in webmail. Note whether the other client is showing an actual server folder, a local folder or a combined view. Before deleting a supposed duplicate, determine whether that action would remove the server message seen in both places.
Worked observation: a sample appears in “All mail” and “Inbox” with the same Message-ID. That is evidence to investigate the views, not an instruction to delete one row. If IDs differ, keep that fact in the report; it still does not explain the cause by itself.