Common causes
- The receiving server's disk or the mailbox quota is full.
- A single message had more recipients than the server allows.
- Many messages from the same sender arrived at once.
- The receiver restricts new senders to small batches.
How to fix it
- Split large mailings into smaller batches.
- Retry later in case the storage problem was temporary.
- Avoid listing many recipients in a single message; send individually.
- Reduce attachment size.
Frequently asked questions
What is a safe batch size?
It depends on the provider. Small, steady batches are accepted far more often than one large burst.
Is the address still good?
Yes, this answer does not say anything about the mailbox. Try again with fewer recipients.