A retail client we advised decided to quadruple email frequency - from one send per week to four - believing more sends would mean more revenue. Within a month:
- Unsubscribe rate tripled.
- Complaint rate crossed the 0.1% threshold.
- Open rate dropped 30%.
- Revenue stayed flat.
The ISPs noticed too. Inbox placement on subsequent sends degraded. The account spent 6 weeks recovering deliverability after 3 weeks of over-sending.
Email frequency has rules, and they're not flexible.
The core rule
Send what the subscriber expected when they opted in. If the signup form said "weekly newsletter," weekly is the promise. Daily isn't aggressive growth; it's a broken contract that triggers unsubscribes and complaints.
Subscribers opt in with a mental model of what they'll receive and how often. Violating that model produces two outcomes:
- Unsubscribe (best case).
- Spam complaint (worst case - damages sender reputation).
Three questions before every additional send
1. Is this content genuinely relevant to the subscriber?
2. Does the subscriber expect to receive this category of email?
3. Is this the right time (not a bad moment, not too close to the last send)?
If any answer is "no," don't send. "The campaign deadline is tomorrow" isn't a good enough reason to break the frequency promise.
Einstein Engagement Frequency
If the client's account has Einstein, use Engagement Frequency instead of guessing. It analyzes each subscriber's historical engagement to predict:
- The ideal email volume per week for this subscriber
- Whether the subscriber is currently being over-contacted (at risk of unsubscribe)
- Whether the subscriber could absorb one more email this week without harm
Output: per-subscriber recommended frequency. Use it to filter the audience on high-volume sends - skip anyone flagged "over-contacted" to protect retention.
Einstein Engagement Frequency is bundled with Marketing Cloud Advanced editions - check if the client has access before promising its use.
Spam filter content signals to avoid
Spam filters look at content patterns regardless of sender reputation. Avoid:
- All-caps subject lines: "50% OFF TODAY ONLY!!!"
- Excessive exclamation marks anywhere in the email
- Spam trigger words: "Free," "Guaranteed," "No risk," "Click here," "Act now"
- Image-heavy with little text: images without enough accompanying text read as spam camouflage
- Missing text version: HTML-only emails are downgraded by many filters
Ironically, the content that's "most aggressive marketing" is also the content that triggers the most spam filters. Copy that reads naturally tends to deliver better.
Volume-based ISP flags
ISPs also watch sending behavior:
- Sudden large volumes from a new IP (before IP warming completed) - flagged as suspicious sender.
- High bounce rate on a send - flagged immediately by receiving ISPs.
- High complaint rate - flagged; reputation damage persists.
- Low engagement across many sends - gradual downgrade to Promotions / Spam.
Ramping a new dedicated IP requires a warming plan - a few thousand sends on day 1, gradually doubling, across weeks. Going from 0 to 500k overnight on a new IP is instantly suspicious.
Content Detective in SFMC
Before sending, run the email through Content Detective. It scans for spam-filter patterns and flags potential issues:
- Trigger words
- Excessive punctuation
- Image-to-text imbalance
- Bad HTML patterns
- Broken links
Content Detective isn't perfect - some filtered content will still deliver, some clean content gets filtered - but running it is a 5-minute safety check that catches the worst offenders.
What "good frequency" looks like
Mid-market B2C retail, healthy setup:
- 1 newsletter per week
- 2-4 promotional sends per month (seasonal / sale events)
- Triggered emails (welcome, cart abandon, post-purchase) on event
- Total: 4-8 emails per month
Subscribers who want more can be offered higher-frequency segments (daily deals, VIP tier) via Publication Lists. Subscribers who want less can downshift the same way. Granular preferences reduce unsubscribes.
Takeaway
Frequency isn't a lever to pull for more revenue; it's a contract with subscribers. Violate it and short-term revenue gains are wiped out by long-term deliverability damage. Use Einstein Engagement Frequency if available, Content Detective every send, and publication-level preferences for granular opt-in. Respect the promise you made at signup.
Balancing revenue goals with deliverability constraints? Our Salesforce team advises on send cadence, Einstein features, and content optimization on production SFMC engagements. Get in touch ->
See our full platform services for the stack we cover.
