What ESP features are needed for dynamic content?

Before you commit to a dynamic content build, check your ESP against the list below. Missing even one of these features usually means the project stalls at the testing stage, which is the expensive one.

Conditional logic inside templates. If-then-else blocks, either via visual editor or via a templating language like Liquid, Handlebars, or MJML with conditionals. Without this, there's no dynamic. Klaviyo, Braze, Iterable, Customer.io, HubSpot, and Salesforce Marketing Cloud all support this. Budget ESPs vary.

Rich subscriber data and custom fields. You need room to store location, tier, last product category, language, and whatever else your rules will reference. Check the field limit (some ESPs cap at 50 custom fields on lower tiers) and the field types supported (strings, numbers, dates, booleans, arrays).

Real-time or near-real-time data sync. If your dynamic content uses purchase history or cart state, the ESP needs to pull that data fresh. Look for webhook ingestion, direct database sync, or a solid two-way integration with your commerce platform. Batch-once-a-day sync kills abandoned cart use cases.

Default and fallback handling. Every conditional block needs a graceful default for "we don't know this value." Check that your ESP supports explicit fallbacks, not just silent empties. If "Hi {FirstName}" renders as "Hi " to unknown subscribers, find a different tool.

Multi-path preview and test sends. This is the one most teams overlook. You need to preview every rule path, not just one rendered version. Look for a preview mode that lets you impersonate a contact (or fake field values) before send. Seed-test groups that hit every condition are a second line of defense.

Content block libraries. Reusable components you can drop into multiple emails save huge amounts of QA time. Without them, every new campaign rebuilds the same logic from scratch, which is where errors creep in.

Rendering QA across clients. Conditional logic sometimes breaks inside Outlook or specific Gmail views. Either the ESP includes built-in rendering tests (via partners like Email on Acid or Litmus) or you need to bolt those on separately.

How to test before you build the whole template.

1. Pick one variable (say, country).
2. Build a two-variant dummy email in your ESP. US version, non-US version.
3. Preview as a US contact and as a non-US contact.
4. Send to seed addresses at Gmail, Outlook, Yahoo, and Apple Mail.
5. Check that both versions rendered correctly and that fallbacks fired when you blanked the country field.

If any step fails, your ESP isn't ready. Fix the infrastructure before you invest in the creative.

Also worth checking before launch: the underlying list. Dynamic content loops through every contact at send, so invalid addresses still consume processing and still bounce. Validate with Review My Emails before the first dynamic campaign so the rendering effort goes to real inboxes.

See how dynamic content works for the underlying mechanism, and what an ESP actually is if you're still picking one.