If mailbox providers feel skeptic of your email volume or sending practices, they may defer your emails. This limiting of or delay in accepting emails is called email throttling.

When you send emails to your recipients, any of the following actions can happen to your emails:

• Delivered - They may get successfully delivered to your recipients' inboxes.
  
• Bounced - They may not be delivered to the recipient end and get returned with an error message stating reason for the bounce.
  
• Throttled - Your emails may not be accepted by the recipient system for some time and will wait in a queue. Zoho MarketingHub will try sending the emails in queue to the recipient system again. This results in delayed delivery of your emails. Sometimes, the recipient system doesn't accept the emails in queue for a long time, and will bounce them instead.
  

Your emails may get throttled if:

• You're new to email marketing or use a new business domain and send emails beyond the threshold limit of your recipient systems . This may make your emails seem suspicious, as there's no history of recipients' previous responses for the sender domain.
  
• You have a negative response such as marking of spam, unsubscribes, and abuse complaints from your recipients in previous emails.
  
• Your previous emails have a high bounce rate.
  
• You send emails to spam traps set by that recipient system.
  
• Your email content and sending practices resemble spam.
  

Though the email restrictions set by recipient systems affect email deliverability, when you plan your emails based on best practices, you can avoid your emails getting throttled. In fact, you can even improve your contact engagement as an added benefit.

How to avoid email throttling

Targeting contacts

Filter frequently communicated contacts, those who are very interested in your emails, and those you are confident will have a positive response.

Target these contacts first with your emails. When you're sure that your emails are not throttled and deliverability is not affected, you can gradually add the less interested contacts.

Warming up your domain with the recipient system

New sender domains are considered cold by mailbox providers (recipient systems). The recipient systems check email sending domains for previous fingerprints or conversation between the sender and recipients.

When you send emails from a cold domain, recipient systems throttle or block the emails, or may even classify them as spam.

Distribute crowded contact base

If your mailing list has most of the recipients concentrated to a few recipient domains, and if those domains are throttling your emails, you should segment your list and distribute the email addresses from the crowded recipient domains to several segments.

For example, Patricia has most of her contacts from zylker.com, and zylker.com is throttling her emails if they're beyond 100 per day. So, she has divided her 1000 zylker.com contact addresses to 10 different segments. These 10 different segments also include email addresses from other recipient domains that don't throttle her emails.

Identify the recipient domains that throttle your emails and segment those email addresses into various lists, as described in the previous point.

Check your bounce error messages in your campaign report. If there are error messages like "Too many emails in short duration", then schedule your emails to email throttling.