Mailjet Team


Email throttling is one of the minor components of email deliverability. This is a technique that consists of carefully adjusting the speed of email/campaign sendings – which will in turn respect the filters of major ISP & receivers across the globe.

The average ISP/receiver utilizes unique thresholds which allows them control email flow and filter out bad email – which is rarely published. As often is the case with email deliverability, it is a great idea to surround one’s self with experienced folks who can redefine delivery speed to various ISPs and receivers.

How it works 

The technique involves configuring several different parameters:

  • The number of emails sent per minute or hour
  • The number of smtp connections per minute or hour
  • The number of emails sent by each connection


According to ISPs and webmails, these parameters are to be used simultaneously or separately. Depending on the email platform you use, you may not always have the opportunity to set these parameters yourself (which could be a good thing). Here are some scenarios:

  • The email sending platform allows you to configure the parameters yourself;
  • It is impossible to optimize the parameters; they are configured by default;
  • The paramenters adjust automatically according to sending conditions.

Reputation and volume

For some ISPs and webmails, the number of accepted connections and the email volume limit may vary depending on your reputation and the number of emails you send. For example, if you suddenly increase the number of emails sent, certain ISPs and webmails will block a portion of your emails.

To detect this type of temporary blockage, if your provider does not do it for you, you must analyze the SMTP error messages like: “Too many connections from your host.”

How does Mailjet handle throttling?

Mailjet adapts sending speed and the number of simultaneous connections to optimize the deliverability of your emails in real time. In this way, you do not have to worry about this aspect of your email campaigns and you benefit from the experience of our deliverability team.