EmailEngine vs Stalwart mail-parser

EmailEngine is a self-hosted email API that connects Gmail, Microsoft 365, and IMAP mailboxes through a unified REST API. It sends webhooks when mailbox messages or state change, and can send mail through the connected account’s SMTP server or provider API. Native integrations use the Gmail API and Microsoft Graph; authentication options include managed OAuth2, service accounts for Google Workspace, Microsoft 365 app-only access, and shared or delegated mailboxes. An optional MCP server, currently in beta, lets connected AI clients search, read, file, draft, and send email with approved access. The admin interface shows sync status and queue details, with a Prometheus endpoint and Grafana dashboard for operations. EmailEngine runs on the customer’s infrastructure, uses Redis for sync metadata, and fetches message bodies on demand rather than storing them. A server and Redis using the noeviction policy are required. The annual subscription is $1,450 a year, excluding VAT where applicable, and includes developer support; each installation can start a full-functionality 14-day trial without signup or a credit card.

Stalwart mail-parser is a free, open-source Rust library for parsing email messages. It supports Internet Message Format RFC 5322, MIME RFC 2045–2049 and other internet messaging RFCs, while attempting to handle messages that depart moderately from those standards. Parsed output includes a MIME tree, text and HTML body lists, and attachments. If one alternative is missing, the library can convert HTML to plain text or plain text to HTML. SIMD kernels accelerate scanning on supported targets, while transfer decoding and charset conversion wait until content is read. Returned strings generally reference the original input message. WHATWG encoding labels are recognized, and the optional full_encoding feature adds legacy multibyte sets including Shift_JIS, Big5 and GB18030. Defaults allow nesting depth 64, 10,000 MIME parts and three decoded nested-message levels. Rust 1.98 is required. No feature is enabled by default; serde adds serialization. The library is licensed under MIT or Apache-2.0 and costs nothing.