These appear when you push or sync a local MBOX archive up to a live mail server and the server's storage quota is full. The mail client cannot upload more until space is freed. Jump to your situation below or work through the methods in order.
Messages like [ALERT] OVERQUOTA, UID max mailbox size exceeded and Maximum Request Size Exceeded all mean the same thing: you are syncing a local MBOX archive up to an IMAP server whose storage quota is full or whose per-request size limit was exceeded. The server refuses to accept more mail until space is freed. This commonly happens when someone imports a large MBOX archive into a mail client set to keep everything synced to a provider with a fixed quota, such as a free 15 GB mailbox. The fix is to free space on the server by purging large attachments and emptying trash and spam in webmail, and to stop the client from trying to push or sync the whole archive, by limiting offline sync to recent mail or keeping the archive in a local-only folder. Upgrading the mailbox storage is the alternative when the mail genuinely must live on the server.
IMAP keeps your local client and the mail server in sync, which means mail you add locally is uploaded to the server. Every server account has a storage quota. When the local archive you are importing pushes the account over that quota, the server returns OVERQUOTA and refuses further uploads.
The related “maximum mailbox size” and “maximum request size” messages are the same problem from the server's side, the account or the single request is too big. The mail is not lost, the server is simply full, so the answer is to free server space or to stop pushing the whole archive up in the first place.
“This one is the server saying I am full, not the file being broken. Someone imports a big archive into an account that syncs everything to the cloud, and the provider's quota fills up, so the upload stops with OVERQUOTA. The fix is two-sided: free real space in webmail by clearing big attachments and emptying trash and spam, and stop the client from trying to shove the whole archive up there, keep the archive local, or limit sync to recent mail. If it truly has to live on the server, buy more storage.”
OVERQUOTA and the maximum-size messages mean the server is full, not that the file is broken. Free real space in webmail by clearing large attachments and emptying trash and spam, and stop pushing the whole archive to the server by keeping it in Local Folders or limiting offline sync. Upgrade storage only if the mail must live on the server.
If the account is well under quota but you still get a size error, a single very large message or attachment may exceed the server's per-message limit. Find and remove or shrink that message, or keep it in a local folder rather than syncing it up. You can also submit your error to us for a tailored fix.
