How to Build High-Converting Email Campaigns with Braze

An email converts when it renders, arrives and is legible. Braze publishes the build constraints that decide all three, and several of them are design decisions rather than development ones. Settle width, layout method and image handling before the creative is signed off. Discovering them in testing means redesigning rather than fixing.

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Key Takeaways

• Braze advises inline CSS and nested tables, and says to avoid div tags, JavaScript and CSS positioning in email templates.
• A template that serves both mobile and desktop should stay under 500 pixels wide, and images must be under 5 MB.
• Use PNG, JPEG or GIF. Braze advises avoiding SVG and WebP because many major email clients do not support them.
• Match the from domain to the sending domain, and put the Reply-To address on a domain you control.
• A plain text alternative lowers your spam score, and alt text with quotation marks needs single quotes.
• Duplicate emails have two documented causes: a duplicated campaign that kept its subject line, and a campaign launched more than once.

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Why does email rendering constrain the design?

Email clients support a narrower set of markup than browsers, so a design that previews correctly can still break on delivery.

Braze is direct about four of these. Use inline style sheets for your CSS. Do not use div tags, because most email clients do not support them, and use nested tables instead. Avoid JavaScript, which does not work with any email service provider. Avoid CSS position: absolute and position: relative in email templates.

We treat that list as a design brief rather than a development checklist. Handing it to a developer after the creative is approved turns a constraint into a rebuild, and anything layered or overlapping is the first design element at risk.

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What are the hard limits on a Braze email?

Four constraints have specific values attached, and three of them shape the design directly.

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Braze recommends three image formats for maximum compatibility:

• PNG
• JPEG
• GIF

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It advises avoiding two newer formats:

• SVG
• WebP

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Many major email clients do not yet support them. That matters if your design system standardised on a modern format for the web, because the same asset pipeline will not serve email.

One counterintuitive instruction sits alongside this. Braze advises against setting heights and widths on images, because doing so can cause unnecessary white space. Fixed dimensions feel safer, and the instruction runs the other way.

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What has to be true before the first send?

The addressing settings are cheap to get right in advance and expensive to correct later.

1. Make sure the from email domain matches your sending domain.
2. Configure a separate Reply-To address on a domain you control, with a mailbox behind it.
3. Avoid Unicode in from addresses, which is not supported.
4. Strip whitespace from addresses before import. Whitespace sent through the API can result in a 400 error.
5. Confirm addresses validate per RFC 2822, the standard Braze applies to addresses targeted through its servers.

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Step two deserves emphasis. Braze describes sending domains and subdomains as configured for deliverability, not as inbound mailboxes. A campaign inviting replies to an address nobody monitors is worse than one that never asks.

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What improves legibility and spam scoring?

Plain text and alternative text do real work, and both are easy to leave until last.

Braze says plain text alternatives are a good way to lower your spam score. Alt text complements images, and it stands in for them when a provider filters images out.

One syntax detail matters here. If alt text contains quotation marks, use single quotes instead of double quotes. Braze also notes that the recipient's email client, not Braze, controls how alt text displays, so write it well and do not pixel-tune it.

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Which markup will Braze reject?

Braze lists tags that are not allowed in email. The list includes:

• script
• iframe
• object
• embed
• meta
• link
• title
• svg

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If you are porting a template built for the web, check that list first. A template that relies on an external stylesheet through a link tag is the obvious candidate to fail.

Analytics tagging has its own rules. Use only one question mark in the final URL, and avoid spaces and special characters. Braze notes that UTM parameters are case-sensitive, so the same campaign tagged in two cases can report as two campaigns.

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Why are users reporting duplicate emails?

Braze describes two causes, and they are diagnosed differently.

The first is a configuration error. A duplicated campaign or Canvas can keep the original subject line, so a user receives two different emails that look like the same one.

The second is a campaign launched more than once. Compare the number of messages sent with the size of the audience before you open a single profile.

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How does this connect to the rest of the programme?

Build constraints decide whether a message renders. What happens next is a different discipline.

Once the template is sound, the content can carry weight. Dynamic content and personalisation are what make a well-built email worth opening, and an onboarding sequence is usually where a template gets its heaviest use. The activation campaigns around it reuse the same template, and so does retention work, which is why a build fault repeats rather than stays local.

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Frequently Asked Questions
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1. Why does my email look different when delivered than in the Braze preview?

Start with CSS positioning. Braze advises avoiding position: absolute and position: relative in email templates.

2. Can I use div tags in a Braze email?

Braze says div tags should not be used, because most email clients do not support them. Nested tables are the documented alternative.

3. Should I set image heights and widths?

Braze advises against it, because fixed dimensions can cause unnecessary white space.

4. Can users reply to a Braze email?

Not to the sending domain, which is not an inbound mailbox. Configure a separate Reply-To address on a domain you control.

5. Why did an email address fail to import?

Whitespace is a likely cause. Braze says addresses cannot include whitespace, and sent through the API it can result in a 400 error. Addresses must also validate against RFC 2822.

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Sources

• Braze, Email guidelines. Retrieved 01 Oct 2026.
• This post draws on a single documentation page. Treat it as a reading of that page plus CustomerIK judgement rather than a survey.
• Written by CustomerIK, a Braze implementation partner.

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CustomerIK is a Braze implementation partner working across onboarding, technical integration, marketing operations and customer data management.

If your emails look different in the inbox than they did in approval, let's talk.

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