Built for the inbox, not the browser
Email templates are 600 to 640 px wide, and images should be supplied at double that resolution and scaled down, so they stay sharp on high-density phone screens. Classic Outlook for Windows renders HTML with a word-processing engine, so background images, some CSS and rounded buttons need fallbacks. Some older Outlook desktop versions show only the first frame of an animated GIF, so that frame must carry the message on its own. Gmail clips any message whose HTML exceeds 102 KB behind a link, and the clipped part often holds the footer, the unsubscribe link and the open-tracking pixel. Templates assembled from generated modules bloat quickly; check the weight before every send.
Dark mode and blocked images
Email apps handle dark mode in different ways: some leave the design alone, some invert parts of it, and some invert almost everything. A logo with dark lettering on a transparent background vanishes against a dark inbox, so give it a light outline or a solid tile. Avoid pure black or pure white text baked into images, which inverts badly. Some corporate and desktop mail clients block images until the reader allows them, so the headline, the offer and the call-to-action must be live text, with the hero image supporting rather than carrying the message. Image-only emails also fail screen-reader users and look suspicious to spam filters.
Variants per segment, measured properly
Generation turns one campaign into a version per segment: a different hero product for each category interest, copy for each lifecycle stage, a language per market, imagery that fits the season where the recipient lives. The studio produces those variants from one approved campaign, with the product kept exact, subject lines and body copy written in 30 languages with approved claims and banned words enforced, and the whole set signed off once with an audit trail. Measure with care. Since iOS 15 in 2021, Apple Mail Privacy Protection has preloaded images and inflated open rates, so judge variants on clicks, conversions and revenue per recipient, against a hold-out group.
Deliverability rules do not care who wrote it
Since February 2024, Gmail and Yahoo have required bulk senders to authenticate mail with SPF, DKIM and DMARC, offer one-click unsubscribe on marketing messages and keep spam complaints below the rate Google publishes; Microsoft brought in similar authentication rules for high-volume senders to Outlook.com from May 2025. Generated content does not change these obligations, but it can change sending behaviour. Many near-identical variants, sudden jumps in volume and image-heavy templates all attract filtering. Increase volume gradually, keep lists clean, and make sure each segment receives something distinct enough to justify the extra send.
Updated 25 September 2026