Balanced provider delivery: avoid unnecessary domain bursts

Sending every Gmail, Microsoft or Yahoo recipient consecutively can create a provider-specific spike even when total campaign volume looks reasonable.

Sorting a list alphabetically by domain can direct a concentrated burst at one provider. That provider sees the per-domain and per-connection rate, not the smoother total shown in your campaign report.

Use a queue designed for delivery

  • Do not group recipients by domain merely for convenience.
  • Interleave providers across normal campaign batches.
  • Respect temporary deferrals rather than retrying aggressively.
  • Use separate provider rate controls only when supported by evidence.
  • Coordinate concurrent jobs sharing the same AuthSMTP account.

Randomisation is not a way to evade provider controls. The objective is a stable, natural flow that prevents your own batching algorithm from manufacturing avoidable spikes.

Key takeaway
Interleave ordinary recipient traffic and apply provider-specific rate controls only where your delivery evidence requires them.
Practical next step

Inspect the next campaign queue in submission order and calculate the largest consecutive block sent to each major recipient provider.

Using AuthSMTP

AuthSMTP manages delivery connections and temporary retries after submission. Your application should avoid creating unnecessary provider-specific bursts in the order and rate at which it submits a large mailing.