When you host email images with Topol, every time someone opens your email, their inbox downloads those images from our servers. That downloading is what we call data traffic. This guide explains exactly how we measure it, how to estimate your own usage, what's included for free, and what happens if you go over.
The short version: Every Topol subscription includes 50 GB of data traffic per month at no extra cost. You only pay if your images are downloaded beyond that.
What "data traffic" actually means
When you build an email in the Topol editor, your images are hosted on our servers rather than being attached to the email itself. Every email client (Gmail, Outlook, Apple Mail, and so on) requests those images from us when the recipient opens the email in their inbox.
Screenshot of the Usage Statistics in your Topol account, with a clear breakdown of your current and past data traffic. Accessible at: https://app.topol.io/usage-statistics
So data traffic isn't about how many emails you send, it's about how many images actually get downloaded. Three things drive that number:
The size of the images in your email (in kilobytes or megabytes).
How many emails you send.
Your open rate, because images are only downloaded when an email is opened.
This is why two campaigns sent to the same list can use very different amounts of traffic: a lightweight email with a few small images uses far less than an image-heavy one, even at the same send volume.
To host images, you need an active Topol.io subscription. If your subscription expires, your hosted images will no longer be available.
How is your data traffic calculated?
We calculate your data traffic with a single, straightforward formula:
Data traffic = Size of images in the email × Emails sent × Open rate
Simply multiply the total image weight of one email by the number you send, then multiply by the share of recipients who open it.
A real-world example
Let's walk through a realistic scenario in which we calculate the total data traffic generated by a single campaign. You do not need to do these calculations yourself; we handle them automatically. However, this should give you a good idea of how the resulting data traffic is actually calculated.
Your campaign:
An email containing 5 images, each 50 KB in size
Sent to 50,000 recipients
With a 50% open rate (0.5)
1) Apply the formula:
Data traffic = Size of images in the email × Emails sent × Open rate
Data traffic = (5 × 50 KB) × 50,000 × 0.5
Data traffic = 6,250,000 KB
2) Convert KB to MB:
Data traffic = 6,250,000 KB / 1024
Data traffic = 6104 MB
3) Convert MB to GB:
Data traffic = 6,104 MB / 1,024
Data traffic = 5.96 GB
This campaign uses roughly 6 GB of data traffic, which is well within the free monthly allowance, with plenty of room to spare.
Use this example as a rule of thumb. A single moderate campaign rarely comes close to 50 GB on its own. The free allowance is typically exceeded only with very large lists, very heavy images, frequent sends, or a combination of all three.
Your monthly allowance
Every Topol subscription includes a monthly allowance of 50 GB of data transfer, free of charge. You'll only ever be billed for traffic that goes above 50 GB. Staying at or under the 50 GB allowance costs nothing.
This allowance:
Resets every calendar month (usage is counted per calendar period, not on a rolling basis).
Covers all the image hosting traffic generated across your campaigns combined.
Pricing for traffic over the allowance
If your image downloads exceed the free 50 GB in a given month, the additional traffic is billed according to the tiered pricing below.
Monthly data traffic | Price |
50 – 75 GB | $20 |
76 – 100 GB | $30 |
101 – 200 GB | $55 |
201 – 300 GB | $100 |
301 – 400 GB | $125 |
401 – 1000 GB | $0.35 / GB |
1TB – 2 TB | $0.3 / GB |
2TB – 5 TB | $0.25 / GB |
5TB – 10 TB | $0.14 / GB |
10TB – 50 TB | $0.12 / GB |
50+ TB* | $0.11 / GB |
*You will be automatically transferred into the Plugin Unlimited tier
Keeping your data traffic down
If you'd like to make the most of your free allowance, the biggest lever is image size. It's the one factor in the formula you control most directly. A few practical habits:
Compress images before uploading. Cutting each image from 100 KB to 50 KB halves the traffic that image generates.
Use appropriately sized images. An image displayed at 600 px wide doesn't need to be 2,000 px wide.
Reuse hosted images across campaigns where it makes sense, rather than re-uploading duplicates.
Because the formula multiplies image size by both send volume and open rate, even small reductions in image weight add up quickly across a large list.
Reach out if you need help!
If you have any questions about your data usage or your current month's billing, please reach out to our support team - we are happy to help.