If you see this “Your email campaign is set to slow sending due to new subscriber validation process. Please read our support article for more information.“ notification in your account it means that your campaign is set to slow sending.
This process happens when new subscribers are uploaded in the account. It starts if you upload more than 5000 subscribers. And it happens only the first campaign to new subscribers is being sent. Meaning that the second campaign to those emails will be sent out right away. But if you will upload new subscribers again then slow sending process will happen again but only to the new subscribers, a campaign to existing subscribers will be sent out immediately.
Slow sending process is necessary to validate new subscribers for ISPs like Gmail, Yahoo, AOL, Microsoft (Hotmail, Outlook, Live) etc. For your delivery to be outstanding the first email campaign is sent in batches.
This process differs for different list sizes. For smaller list sizes it could take up to 4 to 8 hours, for larger lists it could last from 24 till 72 hours.
On individual cases, email campaigns are released from slow sending. Please contact our support team for information at firstname.lastname@example.org