Message features

Whatever you submit over SMTP or the HTTP API, Dispatch preserves the full message and relays it faithfully. These features work across all providers.

Recipients, CC & BCC

Multiple To, Cc, and Bcc recipients are fully supported and parsed independently. BCC recipients receive the message without appearing in the headers other recipients see. The relay log records each recipient class separately.

Attachments

Multiple attachments per message, any MIME type. They’re streamed and preserved via MimeKit. The total message size is bounded by a global and per-relay limit (default 25 MiB); the effective ceiling is also capped to the active provider’s maximum.

Over the HTTP API, attachments use multipart/form-data with one repeatable attachment file field per file - the same convention as Mailgun:

curl -X POST https://host:8025/api/v1/messages \
  -H "Authorization: Bearer $KEY" \
  -F from='you@example.com' -F to='dest@example.com' -F subject='Report' \
  -F text='See attached.' \
  -F attachment=@./report.pdf \
  -F attachment=@./chart.png

The application/json body has no attachment field (matching Mailgun, which is multipart-only for files) - switch to multipart/form-data when you need to attach files. Over SMTP, attachments travel in the MIME message as usual.

Custom headers

Set arbitrary headers - h:<Name> fields (multipart), the headers object (JSON), or simply include them in the raw SMTP message. Raw-MIME providers (Mailgun, Amazon SES, generic SMTP) preserve them verbatim.

Tags

Attach searchable tags (o:tag in multipart, tags[] in JSON) as metadata for filtering in the message log. Tags are Dispatch metadata, not email headers.

What’s recorded

Every message is logged with its recipients, subject, the relay and routing rule used, the provider’s response and message ID, duration, ingest source (SMTP / API / dashboard test), source IP, attachment count, and more - all searchable and filterable in the dashboard. See Health & metrics for aggregate stats.