Known issues

The transport layer is ported from upyo 0.7.0 and keeps its behavior, bugs included, until each bug is fixed on its own with a test. This page lists the ones still open; the fixed ones are in the changelog.

HTTP providers and JMAP

• JMAP on Node 24: an authentication rejection (401) during the upload of a raw message whose size is not known ahead becomes a retryable network error, as Node's fetch reports an early answer to a streamed body so. Requests, and raw messages of a known size up to 4 MiB, go from a buffer and are not affected.

Deno

• Deno's fetch (2.9.6) sends a request again when a reused HTTP/1.1 connection closes before its answer. When the provider took the request before the connection was lost, the message goes twice; on Node and Bun the same failure is reported as of unknown delivery (deliveryUnknown) and not retried. Pass the HTTP transports and JMAP a fetch on a client that keeps no idle connection, Deno.createHttpClient({ poolMaxIdlePerHost: 0 }), as getting started shows. The providers that take an idempotency key, which the transport sends with every message (Resend, Lettermint, Brevo, Azure), see the second request as the first and do not send the message again.