Broadcast (SendMulti)

Sometimes you need to send the same notification to many users — a weekly digest, an incident announcement, a new-feature rollout. That's SendMulti.

Basic usage

users := []notification.Notifiable{u1, u2, u3, ...}

notifier.SendMulti(ctx, users, WeeklyDigest{Week: "2026-W16"})

Behavior:

• Each recipient's Via() is resolved independently (they can differ — one user wants mail + database, another wants only database).
• Sends are enqueued on the worker pool (or executed synchronously in sync mode).
• Retry, rate limiting, and error handling apply per-send just like Send().

Chunking large sends

For tens-of-thousands of recipients, don't build a single giant slice — that uses a lot of memory and pressures the queue. Process in chunks:

const chunkSize = 500

for i := 0; i < len(allUsers); i += chunkSize {
    end := i + chunkSize
    if end > len(allUsers) { end = len(allUsers) }

    notifier.SendMulti(ctx, allUsers[i:end], WeeklyDigest{})
}

Provider-specific batching

Some providers have batch APIs:

• Mailgun — batch_size=1000 recipients per API call, same content.
• SendGrid — personalizations array up to 1000 per request.
• FCM — multicast up to 500 tokens per request.

The drivers use these automatically when SendMulti detects same-content sends across the same channel. If you use per-recipient content (personalized subject lines, etc.), they fall back to single-recipient calls.

When not to use SendMulti

• Rate-limited channels (SMS, WhatsApp) — you'll hit provider caps fast. Use a slower pipeline, not SendMulti.
• Highly personalized content — if every recipient gets meaningfully different data, the batch optimization disappears and you're just using Send in a loop with extra abstraction.

Per-recipient error handling

Errors from individual recipients fire the usual OnError callback, including which notifiable failed:

OnError: func(ctx context.Context, err notification.Error) {
    log.Error("send failed",
        "notifiable", fmt.Sprintf("%T/%v", err.Notifiable, err.Notifiable),
        "channel",    err.Channel,
        "err",        err.Err,
    )
}

One recipient failing does not abort the rest.

Ordering

SendMulti does not guarantee ordering. If you need ordered delivery (rare for notifications), send one-by-one synchronously. For everything else, assume sends complete in worker-pool order.