Does volume cause blocking?

There seems to be a never ending debate about volume and how it affects delivery and revenue. I regularly get questions asking if ISPs block senders just for volume.
The answer is no. Unless you’re actually sending enough mail to overwhelm the incoming infrastructure, something that’s difficult on today’s internet, you’re unlikely to be blocked due to simply sending a high volume of mail.
Sending mail recipients don’t want, or mail that looks like spam, that will get the mail blocked or filtered.

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Does mail volume contribute to blocking?

There are two extreme opinions I see among marketing agencies and email senders when it comes to volume.
One group seems to think that volume alone triggers blocks. Another group thinks volume never affects delivery.
As with many things in delivery reality is at neither extreme.
Sending lots of mail isn’t the problem. Sending lots of mail your recipients aren’t interested in getting is the problem. Last year during the US political elections the Obama campaign, for instance, sent lots and lots of mails. Their list was an order of magnitude larger than the Romney campaign and there were days they were sending 10s of mails per subscriber. It was a deluge. But they were smart, and they did a lot of data mining and they did it in a way that got recipients to act on the mail. That mail was a deluge, but it was a wanted deluge by most of the receivers.
For a lot of vendors, too, increasing volume does increase response and revenue and all the things you want to drive with email marketing. But there will be people who don’t like the increase in volume. If they’re not valuable customers, no great loss. If they are valuable customers, then the increase in volume may drive a decrease in revenue.
In terms of inbox delivery, it’s not the volume it’s how wanted the mail is. Send wanted, interesting and engaging mail, you can send dozens of times a day.
No, volume alone doesn’t contribute to delivery problems.

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What is a dot-zero listing?

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Some email blacklists focus solely on allowing their users to block mail from problematic sources. Others aim to reduce the amount of bad mail sent and prefer senders clean up their practices, rather than just blocking them wholesale. The Spamhaus SBL is one of the second type, using listings both to block mail permanently from irredeemable spammers and as short term encouragement for a sender to fix their practices.
All a blacklists infrastructure – and the infrastructure of related companies, such as reputation monitoring services – is based on identifying senders by their IP addresses and recording their misbehaviour as records associated with those IP addresses. For example, one test entry for the SBL is the IP address 192.203.178.107, and the associated record is SBL230. Because of that they tend not to have a good way to deal with entities that aren’t associated with an IP address range.
Sometimes a blacklist operator would like put a sender on notice that the mail they’re emitting is a problem, and that they should take steps to fix that, but they don’t want to actually block that senders mail immediately. How to do that, within the constraints of the IP address based blacklist infrastructure?
IP addresses are assigned to users in contiguous blocks and there’s always a few wasted, as you can’t use the first or last addresses in that range (for technical / historical reasons). Our main network consists of 128 IP addresses, 184.105.179.128 to 184.105.179.255, but we can’t put servers on 184.105.179.128 (as it’s our router) or 184.105.179.255 (as it’s the “broadcast address” for our subnet).
So if Spamhaus wanted to warn us that we were in danger of having our mail blocked, they could fire a shot across our bow without risk of blocking any mail right now by listing the first address in our subnet – 184.105.179.128 – knowing that we don’t have a server running on that address.
For any organization with more than 128 IP addresses – which includes pretty much all ISPs and ESPs – IP addresses are assigned such that the first IP address in the range ends in a zero, so that warning listing will be for an address “x.y.z.0” – it’s a dot-zero listing.

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