SMTP Labs

SMTP Labs, Inc. offers SMTP Labs, an email testing platform for developers who need to inspect and validate messages without sending them to real inboxes. The service receives email through standard SMTP and lets users access it through IMAP, POP3, a web interface, or a REST API. It works with existing mail clients and CI tools, without requiring a vendor SDK, and supports custom domains, disposable accounts, catch-all addresses, and plus-addressing.

Developers can review message headers, MIME structure, raw RFC 5322 source, HTML previews, and plain-text content. The platform also checks SPF, DKIM, and DMARC results for inbound messages and provides deliverability audits covering sender configuration, HTML structure, links, and content patterns associated with spam filters. Teams can use it for automated assertions, end-to-end email flows, signup testing, client previews, and authentication checks in staging. New messages can be delivered through real-time server-sent events, while retention settings keep messages for a plan-defined period of up to 90 days.