Introduction
You can send marketing and transactional emails together, but doing it under one identity with no guardrails often creates delivery issues for critical emails like OTPs and password resets. The problem is not that marketing email is bad. The real issue is that marketing volume and complaint behavior are different from transactional traffic, which makes problems harder to isolate when everything shares the same sender identity.
This setup guide is for SaaS and development teams that send both campaigns and product-critical emails. The safest approach is to separate streams with different subdomains, keep authentication consistent, and define clear rules for unsubscribes and suppression. If you are setting up your environment, you can review the Mailcub documentation first, and then test your transactional stream with the Transactional Email product.
The goal is simple: protect reliability first, then scale growth safely.
Quick Answer
- Yes, you can send marketing and transactional emails together, but use two subdomains to separate risk (for example, one for marketing and one for transactional).
- Authenticate each stream properly with SPF, DKIM, and DMARC, and keep the identity consistent for each stream.
- Marketing needs unsubscribe handling and list hygiene, while transactional needs strong reliability, logging, and event tracking.
- Use suppression for hard bounces and complaints, and do not keep retrying invalid or complaining recipients.
- Monitor each stream separately so you can isolate incidents quickly.
Why This Matters
Marketing email usually has higher sending volume and a higher chance of complaints than transactional email. Transactional messages are product-critical and time-sensitive, which means even a small deliverability issue can affect logins, password resets, receipts, and security alerts.
When both types of email share one identity, marketing problems can spill over and affect transactional delivery. That is when OTPs start landing in spam and debugging becomes slow because there is no clean way to isolate the cause. A two-stream setup makes issues easier to detect, easier to explain, and easier to roll back.
Use Two Subdomains for a Safe Setup
The safest default pattern is to use two streams and two subdomains:
- Transactional: tx.example.com (or notify.example.com)
- Marketing: news.example.com (or updates.example.com)
This split helps isolate reputation and keeps monitoring clean. It also reduces the chance that a marketing spike impacts your most important emails.
Avoid DMARC Surprises with Consistent Identity
DMARC checks alignment between the From domain and your authentication identities. If you switch From domains or mix identities across streams, you can create confusing situations where DKIM passes but DMARC still fails.
Use these practical rules:
- Make sure each stream’s From domain aligns with DKIM signing and your intended SPF identity.
- Treat marketing and transactional as separate identities, even if they belong to the same brand.
- Keep the setup stable once it is working, especially for transactional mail.
Step-by-Step Safe Setup
Step 1: Classify Your Email into Two Buckets
Start by separating your email into two main categories.
- Transactional: OTP and login codes, password resets, receipts, and security alerts
- Marketing: newsletters, promotions, win-back campaigns, and announcements
If a message type does not fit clearly, create a third category like product notifications and decide whether it behaves more like marketing or transactional.
Step 2: Choose Stable Subdomains
Pick your sending subdomains and keep them stable. Renaming subdomains later can force re-warmup and create confusion in logs and monitoring.
Good defaults are:
- Transactional: tx. or notify.
- Marketing: news. or updates.
Step 3: Authenticate Each Stream Separately
For each subdomain, publish and verify the correct authentication records:
- SPF authorization
- DKIM keys
- DMARC policy
Keep each stream internally consistent. The From domain, DKIM signing identity, and sending infrastructure should match the stream you are using.
If you are configuring this for the first time, use the Mailcub docs to validate your domain setup before sending production traffic.
Step 4: Separate Unsubscribe and Suppression Behavior
This is one of the most important rules in a mixed setup.
- Unsubscribe applies to marketing and optional notifications.
- Suppression applies to hard bounces and complaints for operational safety.
Do not let marketing unsubscribes block critical security or transactional emails. At the same time, do not ignore suppression signals or you will continue sending to invalid or complaining recipients.
Step 5: Warm Up Marketing Carefully
Marketing warm-up is where many teams damage deliverability. Start with your most engaged users, increase volume gradually, and watch bounce and complaint changes daily during the ramp.
Keep your transactional stream steady and stable while marketing ramps. Do not change identities during this phase unless you absolutely have to.
Step 6: Monitor Each Stream and Keep a Rollback Plan
Track metrics separately for marketing and transactional streams so you can isolate issues fast.
Monitor per stream:
- Delivery rate
- Bounce rate
- Complaint rate
- Deferrals and timeouts
- User reports such as “OTP missing”
Keep a rollback plan ready:
- Pause marketing sends quickly if risk increases
- Revert to the last known-good From identity if needed
- Use logs and event tracking to confirm what happened by timestamp
To support this setup, you can test tracking and delivery flow using the Mailcub Transactional Email service. If you are comparing options before rollout, review the pricing page for planning.
Safe Setup Options and Risk Level
| Setup option | When it’s okay | Risk level | How to make it safer |
|---|---|---|---|
| One domain for everything | Very low volume, no bulk sending | High | Move marketing to a subdomain |
| Two subdomains: tx. + news. | Most SaaS products | Low | Authenticate and monitor each stream separately |
| Separate domains | Special cases, brand split | Medium | Use clear UX and strict identity rules |
| Dedicated IP for marketing | High volume with strong hygiene | Medium | Warm up slowly and keep transactional separate |
| Dedicated IP for transactional | High criticality with stable volume | Low | Use change control and consistent identity |
Common Mistakes to Avoid
- Sending promotions and OTPs from the same From domain with no separation
- Changing subdomains frequently, which forces re-warmup and breaks identity continuity
- Treating unsubscribes as global and blocking critical transactional messages
- Ignoring hard bounces and complaints instead of suppressing them
- Monitoring only general deliverability and not stream-specific behavior
Troubleshooting
Problem: After a marketing campaign, OTP emails started landing in spam
Use this checklist to isolate the issue:
- Confirm that transactional email uses a separate subdomain (such as tx.)
- Verify authentication alignment on the transactional identity
- Pause the marketing ramp if complaints or bounces spiked
- Check the transactional From name and address consistency (it should look product or security-focused, not promotional)
- Use event logs and timestamps to confirm what happened
Problem: A user unsubscribed but still received emails
This usually happens for one of these reasons:
- The unsubscribe was applied only to one list or one system
- The user is still receiving transactional or critical mail, which may be expected
To fix this, clearly define your email categories, apply unsubscribe checks to marketing templates, and document what “unsubscribe” means inside your product experience.
FAQ
Can I send marketing and transactional emails together from one domain?
You can, but it increases risk because marketing volume and complaints can affect the shared identity. A safer setup is to separate the streams with subdomains.
What is the safest subdomain setup for marketing vs transactional?
A common and safe setup is tx.example.com for transactional email and news.example.com for marketing email. Authenticate each one and monitor them separately.
Do unsubscribes apply to transactional emails?
Unsubscribes usually apply to marketing and optional notifications. Critical transactional emails such as security alerts and receipts are typically still sent, but your policy should be clearly defined.
How do complaints in marketing affect transactional delivery?
If both streams share the same identity, marketing complaints can reduce trust signals and hurt transactional inbox placement. Separate subdomains help reduce this spillover risk.
What should I monitor per stream?
Track delivery, bounces, complaints, deferrals, timeouts, and user reports for each stream. This helps you isolate and fix issues quickly.
When do I need a dedicated IP?
Dedicated IPs can help when you have high and stable volume with strong list hygiene. They still need careful warm-up and should not be treated as a shortcut for deliverability.
Conclusion
You can send marketing and transactional emails together safely if you treat them as separate streams with separate identities. Use subdomain separation, authenticate each stream, define unsubscribe and suppression rules clearly, and monitor performance per stream so you can isolate incidents quickly.
Before your next campaign, use the documentation page to confirm your setup, test delivery with the Transactional Email product, and review the Mailcub pricing page if you are planning your rollout.