mailboxquotas

Mailbox quotas are storage limits imposed on individual mailboxes in an email system. They regulate the maximum amount of disk space a mailbox may consume, including messages, attachments, and metadata. The term mailboxquotas is used in some ecosystems to refer to per-mailbox storage limits. Quotas help manage disk resources, ensure service availability, and prevent a single mailbox from affecting others.

Quotas are enforced by the mail server. The system tracks the size of a mailbox and compares it to its assigned limit. Some systems use soft quotas, which generate warnings and allow temporary delivery, and soft limits can trigger a grace period. Hard quotas enforce a strict limit and may reject new messages or quarantine them when the limit is reached. Quotas can be configured per user or per mailbox and can be expressed in bytes, kilobytes, or as a percentage of a configured maximum.

Implementation varies by platform. Mail servers such as Dovecot, Cyrus, Microsoft Exchange, and Postfix often implement quotas through modules or built-in features. Quota accounting may count only active messages, or may include deleted items that have not been purged. Administrators monitor usage with reporting tools, alerting when thresholds are approached, and may adjust quotas as needed.

Impact and considerations: quotas affect user experience, service reliability, and backup planning. Tight quotas can force users to archive or delete mail, while generous quotas reduce user friction but require more storage. Standards for quotas are not universal; configurations and reporting formats differ across platforms.