EmailEngine is a REST API that gives applications access to Gmail, Microsoft 365 and IMAP mailboxes. It reads, sends and synchronises messages for many user accounts at once. Sync metadata is kept in a Redis store that the customer controls, and message bodies are fetched on demand from the original mailbox. The product is installed on the customer's own infrastructure and is not a cloud service. A subscription is required for use.
EmailEngine is developed and licensed by Postal Systems OÜ, based in Tallinn, Estonia, so the vendor is established within the EU. The vendor states that it has no access to customer mailboxes and that stored credentials and tokens are encrypted with AES-256-GCM. Because the software runs on the organisation's own servers, data residency and GDPR compliance depend on how that environment is run, and the vendor makes no certification claim for the product itself. The source code can be read and audited, but the licence is a commercial source-available agreement rather than an open source licence.