A mailstore is the server-side repository where an email platform keeps messages, attachments, folders, and related account data. In many systems, it is the main storage layer behind the webmail interface and mailbox services, so users see a mailbox while the server holds the actual content.
Mailstores matter because they concentrate sensitive information in one place. If an attacker gains access through stolen credentials, a web flaw, or remote code execution on the mail server, the mailstore can become a high-value target for bulk message theft, attachment exfiltration, mailbox tampering, or search for passwords, tokens, and internal documents. Defenders protect mailstores with strong authentication, least-privilege service accounts, encryption at rest, access logging, and monitoring for unusual reads, exports, or file-level changes. In incident response, checking the mailstore is often essential to determine what data was exposed and whether messages or attachments were altered.