Deliverability
Primary inbox or Promotions tab: what actually decides the placement
8 October 2025 · 8 min read
The Promotions tab is not the spam folder. It is where Gmail puts mail it has classified as promotional — and for many senders it performs perfectly well, because that is where subscribers go looking for offers.
Still, placement is worth understanding, and one technical constraint in particular is worth fixing regardless of tab.
What influences categorisation
- Per-recipient engagement history — the single strongest signal, and one you cannot configure.
- Bulk-sending patterns: identical content to a large list reads as promotional.
- Content structure: many images, prominent calls to action and heavy tracking.
- The presence of promotional headers and list-management headers.
- Whether the recipient has previously moved your mail between tabs.
The 102KB truncation ceiling
Gmail clips messages whose HTML exceeds roughly 102KB, showing a 'View entire message' link. Anything after the clip — including your unsubscribe footer and tracking pixel — is not rendered for most readers, which suppresses measured opens and hides the compliance footer.
Keep HTML under about 100KB: strip unused CSS, avoid base64-embedded images, host images externally, and remove editor comment blocks before sending.
| Cause | Typical cost | Fix |
|---|---|---|
| Base64-embedded images | 50–500KB | Host images and reference by URL |
| Unused framework CSS | 20–80KB | Inline only the styles used |
| Deeply nested table layouts | 10–30KB | Simplify to a single-column structure |
| Editor metadata and comments | 5–20KB | Strip before sending |
How to influence placement legitimately
Segment so that content matches intent; send transactional and marketing mail from separate subdomains; write plain, specific subject lines; and ask engaged subscribers directly to move you to Primary if it matters to your programme. Attempting to disguise promotional mail as personal correspondence raises complaint rates, which is strictly worse than the Promotions tab.
Key takeaways
- The Promotions tab is a category, not a penalty.
- Per-recipient engagement dominates categorisation.
- Keep HTML under about 100KB or Gmail clips your footer and pixel.
- Separating transactional from marketing streams helps placement.
Sources
Put this into practice with HTsend
Everything in this guide is built into the platform: authenticate a sending domain, clean your list before you send, and watch inbox placement in real time.
