What Is Email Throttling and How to Use It

When you send a high-volume campaign all at once, you risk flooding ISP servers with more traffic than they will accept — triggering deferrals, bounces, or spam filtering in the process. Email throttling is the practice of spreading a campaign's delivery across a controlled time window, preventing these problems before they happen.

Why Throttling Is Important for Large Sends

ISPs and inbox providers set limits on how many emails they will accept from a single sender in a given period. Exceeding these limits can result in:

• Emails being deferred or outright rejected by the receiving mail server

• Sudden sending spikes being flagged as suspicious, triggering spam filters

• Rising bounce rates that signal poor list quality to inbox providers

• Your sending domain or IP appearing on blocklists

Throttling prevents each of these outcomes by keeping your sending rate within safe thresholds throughout the campaign.

How Mailzzy's Throttling Works

When you launch a large campaign, Mailzzy automatically divides your contact list into batches and schedules those batches to be sent over a defined period at intervals that comply with ISP guidelines. This process is fully automated — you do not need to manually configure batch sizes or sending intervals.

When Throttling Matters Most

• Campaigns going out to 50,000 or more recipients

• Sends from a relatively new or recently warmed-up sending domain

• Campaigns sent from a dedicated IP that is still building its reputation

• Lists containing recipients spread across many different inbox providers

What to Expect During a Throttled Campaign

Because emails are released in batches over time, not every recipient will receive the campaign at the same moment. For most large campaigns, the majority of emails arrive within the first few hours. Very large sends may take longer.

Your campaign report updates in real time throughout the delivery window, so you can monitor progress without waiting for the send to fully complete.