Banner Specifications
Standards to meet to ensure optimal display on all email clients (Outlook, Gmail, Apple Mail…).
Standard formats
| Format | Dimensions (W × H) | Typical placement |
|---|---|---|
| Large Banner (Leaderboard) | 600 × 150 px (sometimes 640 px) | Header or core of email — most impactful format |
| Block (Rectangle) | 300 × 250 px | Side column or email footer — compact format |
Technical constraints
| Criterion | Specification |
|---|---|
| File type | JPG, PNG, or GIF |
| Color mode | RGB |
| Maximum size | 150 KB — recommended < 80 KB for fast loading on mobile |
Animated GIFs — first frame rule
Animated GIFs are accepted, but Outlook (desktop versions) only displays the first image.
The main information and the Call-to-Action must imperatively appear on the first frame.
Design best practices
White background: add a border
If your banner has a white background, add a 1 px gray border (#cccccc) all around to clearly delimit it against the email background.
On mobile, a 600 px banner is reduced to ~350 px wide. Avoid fonts that are too thin or too small — recommended minimum size: 16 px.