IMAP diagnostics
OVERQUOTA: the destination mailbox is out of space
How it looks in the log
a3 NO [OVERQUOTA] Not enough disk quota (0.001 + 12.400 GB)The destination mailbox is full and the server refuses the next message. The transfer stops there; everything already copied stays put.
Causes, most likely first
- The source is larger than the destination quota. The classic case: 12 GB moving into a 5 GB plan.
- Gmail and Google Workspace share quota with Drive and Photos, so there is less room for mail than it appears.
- Spam and Trash are included in the run and often account for the first few gigabytes.
- On hosting, per-mailbox quota is set separately from account quota and is often much lower.
How to fix it
- Measure the source before starting — it is a separate free step and takes a minute.
- Compare that figure with actual free quota at the destination, not the plan on paper.
- Exclude Spam, Trash and, on Gmail, [Gmail]/All Mail. That is often enough.
- Raise the destination quota or split the mail across two mailboxes.
- After raising the quota just run the transfer again: the repeat copies only what is missing.
FAQ
Common questions
What happens to already-copied messages?
They stay. A repeat run compares what already exists at the destination and copies only the remainder, so nothing duplicates.
Gmail shows free space but I still get the error — why?
Gmail quota is shared with Drive and Photos. The free space shown in the mail interface may refer to total storage that other services have already consumed.
Other errors
Find out how big your mailbox is. It costs nothing.
Connect two servers, look at the size and decide. Or take the client and keep everything on your side.
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