Glossary
Gigabyte (GB)
A unit of storage, about a billion bytes, used for mailbox size and attachment limits.
ValidReach Team · Updated 2026-10-26
In practice
Providers give each mailbox a storage quota in gigabytes, and a full mailbox causes soft bounces. Message size limits are far smaller, in megabytes.
Verification and sending
A mailbox that is over quota may reject mail temporarily, which a verifier can report as unknown rather than invalid.