Pauses, Retries and Stopping a Campaign

Imagine a campaign in full swing, and suddenly Gmail starts answering "this is spam". You could keep sending and hope it passes. But the provider remembers every such email, and within an hour it is sure your domain sends spam. It will meet your next campaign with that same opinion.

So Estismail does it differently: at the first signs of trouble, sending to that provider freezes at once. Not the whole campaign, only the part going to that provider. Mail.ru, Yandex and the rest keep receiving emails as if nothing happened. And the emails for Gmail simply wait in the queue: they are not lost and not skipped.

What counts as trouble

Most often it is "spam" or "blocked" rejections. When they pile up one after another, there is no point waiting for more. If the provider says outright that the sender is banned, sending stops from the very first answer.

Here is how we count: two such rejections within one minute, or two "spam" rejections among the first 500 emails to the provider, or 1% of "spam" rejections once more than 200 emails have been sent.

The second trouble is addresses that do not exist. Many of them mean the list is stale, and the provider can see it. When, already among the first 50 emails, every tenth goes nowhere, there is no reason to wait any longer. After 200 emails the threshold is 5%, and for those who sent no campaigns in the 90 days before, it is stricter, 3%.

Sometimes rejections come only through one or a few of our public servers, while the same emails get through the others. Then the problem is not your campaign, and it does not need a pause: those servers simply stop sending it. More in the article on sending servers and public servers.

How long a pause lasts and what comes next

The first pause is short, 10 minutes. Often that is enough: the cause was temporary and the provider calmed down. But before continuing, Estismail looks at what happened during those minutes. If "this is spam" complaints about this campaign's emails became noticeably more frequent than usual for your domain, or new rejections kept arriving, it is too early to continue. Rejections in the first 2 minutes of the pause do not count: they are answers to emails sent before it.

To be precise: for a new domain, "noticeably more" means 5 or more complaints, and at least 0.05% of what was sent. For a domain with a history, it means 0.1% or more, and twice its usual level.

If all is quiet, sending starts again, and it starts carefully. Not at the speed where it stopped, but with a test batch of 50 emails, then from 50 emails per minute, one and a half times faster every calm minute, but never above 600 emails per minute. After 60 minutes with no new rejections the speed grows by your domain rating again, as at the start of the campaign, and the pause count resets.

If the provider is unhappy again, the pause is longer: 30 minutes, and after it one more, 120 minutes. With each pause the provider has more time to cool off, and we get more certain that it is not a temporary glitch.

On the chart in the campaign report all this looks like the line dropping to zero and a new "test batch" after it. Often that is the only thing you will notice.

When we have to stop completely

If the provider keeps rejecting emails after the third pause, sending to it in this campaign stops completely. This is not a punishment but protection for your domain: every further email the provider considers spam worsens its opinion of you, and your next campaigns would pay for it.

Unsent emails stay in the campaign report as "not sent". The other providers get the campaign in full. You will not get a separate email about a stop, everything is visible in the report, and our support learns about every stop right away. What you can do in that situation is explained in the article on campaign report and what to do.

When a provider doesn't reject but asks you to slow down

There is an answer softer than a rejection: the provider defers some emails and effectively says "slower, please". There is no need to stop here. Estismail resends the deferred emails by itself and lowers the speed. If 10% of addresses or more are deferred within a minute, the speed is halved, but not below 50 emails per minute. If the provider asks for this minute after minute, the top speed is also lowered for 30 minutes, and if the request repeats, the speed is halved once more. Then the ramp-up continues from the new speed.

Two cases still need a pause. If the provider deferred half of the test batch, there is nowhere slower to go than the test batch. And Gmail with the answer "421 4.7.28", about an unusual flow of emails, gets a pause at once, from the first such answer: that is how Gmail signals that it already dislikes the flow of emails.