Finding specific things
A mail account open for a decade holds gigabytes of attachments you will never open again.
Apple Mail: View → Sort By → Size, or add a Size column in the message list (View → columns). Largest messages float up — almost always the ones with attachments.
du -sh ~/Library/Mail 2>/dev/null
du -sh ~/Library/Containers/com.apple.mail 2>/dev/null
Both, since the split varies by macOS version. Tens of gigabytes is routine.
System Settings → General → Storage → Mail lists large attachments with delete buttons — the friendliest route, and it spans accounts.
Mail → Settings → Accounts → [account] → Account Information → Download Attachments. Set archival accounts to Recent or None. Existing downloads then clear on the next sync, and the messages stay — only the local attachment copies go.
Select a message → Message → Remove Attachments. The text stays; the file leaves. Good for the newsletter with a 30 MB PDF you will never reopen.
For IMAP/Exchange accounts the attachments also live on the server; removing local copies frees your Mac but not your quota. For the server side, delete the messages themselves or use the provider's own large-mail tools.
Before deleting wholesale, the attachment you actually want is inside the Mail container where Spotlight will not show it — the mail-attachments article covers extracting it. Save anything worth keeping out to real folders, then clear with a clear conscience.
Sort Mail by Size, or use System Settings → Storage → Mail which lists large attachments with delete controls.
No — Message → Remove Attachments keeps the message text and drops only the files.
Everywhere keeps track of every file on your Mac, including the folders Spotlight hides and drives you have unplugged. Free for a day, then $19 once.
Version 2.20.3 · macOS 13+ · 4.7 MB · notarised