Email is the one remaining place where a design has to work in clients that ignore most of modern layout, strip styles, block images by default and render the same code three different ways. A beautiful mockup means almost nothing here. What matters is what arrives in the inbox of somebody using an old desktop client with images off, and the difference between a competent supplier and a decorative one is entirely in that question.
Ask which clients they test in, by name
A competent email designer names the clients they test against and has a testing service. One who describes the design and not the testing is producing a mockup. Ask specifically what happens in a client that does not support modern layout, and what the fallback looks like, because that fallback is what a meaningful share of your list will actually see.
Assume images are blocked and design for it
Many recipients see no images until they choose to load them, which means an email built as a single large image is blank. Real text, sensible alternative text, a visible and legible call to action without images, and a design whose meaning survives their absence. This is the most common expensive failure in email design and it is entirely avoidable.
Accessibility is not optional and it helps deliverability
A single-column layout that reflows, real text at a readable size, sufficient contrast, meaningful link text and a proper language attribute. Screen readers and older recipients need it, and mail providers treat well-formed messages better than image-heavy ones. It is the rare case where the accessible version is also the one that performs best.
A template system beats a series of one-off designs
What you want at the end is a set of modular blocks your team can assemble in the platform without a designer: a header, a hero, a product block, a text block, a footer with the legal requirements already in it. That is what makes email cheap to run afterwards. A supplier delivering beautiful individual emails has sold you a dependency.
Dark mode changes the design whether you plan for it or not
Many clients now invert or adjust colours automatically, and logos on white backgrounds, coloured text and images with white edges all behave badly. Ask to see the design in dark mode before approving it. It is a five-minute check that prevents the most common modern complaint about email design, and most suppliers still do not do it unprompted.
Questions people ask about email design service
Why is email design harder than web design?
Because mail clients ignore much of modern layout, strip styles, block images by default and render the same code differently. What matters is what survives, not what the mockup looks like.
What should we ask a designer first?
Which clients they test in, by name, and what the email looks like with images blocked. Both answers separate somebody building for the inbox from somebody producing a picture.
Should we get individual designs or a template system?
A system of modular blocks your team can assemble without a designer. Individual designs are more beautiful and leave you dependent on the supplier for every send.
Does dark mode matter?
Yes. Many clients invert colours automatically and logos, coloured text and images with white edges behave badly. Ask to see it in dark mode before approving; it takes five minutes and is routinely skipped.