Email Delivery
Synapse delivers email with DKIM authentication over a verified sending domain. Out of the box, that's Synapse's shared pyrx.tech domain, which is already verified and DKIM-signed — so you can go live and send with no setup. Verifying your own custom domain is an optional upgrade for better deliverability and branding. This page covers how to set up a custom sender domain, understand delivery infrastructure, and maintain a healthy sender reputation.
Sender Domains
You don't have to verify a domain to send. Every workspace can send on Synapse's shared pyrx.tech domain, which is already DKIM-signed. Verifying your own domain is an optional upgrade — it proves ownership of your domain and enables DKIM signing on it, which improves deliverability and puts your brand in the "From" address.
Adding a Custom Domain
- Navigate to Settings > Domains in the dashboard
- Click Add Domain and enter your domain (e.g.,
notifications.acme.com) - Synapse provides DNS records to add to your domain registrar
- Add the records and click Verify
Required DNS Records
| Type | Name | Purpose |
|---|---|---|
| TXT | _synapse.yourdomain.com | Domain ownership verification |
| CNAME | DKIM selector | DKIM signing (email authentication) |
Use a subdomain for transactional email (e.g., mail.acme.com or notifications.acme.com). This isolates your transactional sender reputation from your corporate domain.
DKIM Authentication
DomainKeys Identified Mail (DKIM) adds a cryptographic signature to your emails. Receiving mail servers use it to verify the email was actually sent from your domain and wasn't tampered with in transit.
Synapse signs all outgoing email with DKIM automatically. On the shared pyrx.tech domain this is already in place with no configuration. When you verify your own custom domain, Synapse signs with DKIM on your domain instead — again, no additional configuration is needed.
IP Warming
If you're migrating from another platform or starting with a new sending domain, you may need to warm up your sending reputation gradually.
What is IP Warming?
Email providers (Gmail, Outlook, Yahoo) track sending patterns. A new sender suddenly sending thousands of emails looks suspicious. IP warming gradually increases your daily send volume so providers build trust in your domain.
Recommended Warming Schedule
| Day | Daily Send Volume |
|---|---|
| 1--2 | 50--100 |
| 3--4 | 200--500 |
| 5--7 | 500--1,000 |
| 8--14 | 1,000--5,000 |
| 15--21 | 5,000--10,000 |
| 22--30 | 10,000--50,000 |
| 30+ | Full volume |
During warming, send to your most engaged contacts first (recent openers, clickers). High engagement signals during warming dramatically improve long-term deliverability.
Deliverability Best Practices
- Send DKIM-signed -- the shared
pyrx.techdomain is already DKIM-signed; for production, verifying your own domain adds DKIM on your brand and isolates your reputation - Use a subdomain -- when you add a custom domain, separate transactional email from marketing email
- Monitor bounce rates -- hard bounce rate above 2% damages reputation
- Handle unsubscribes -- honor unsubscribe requests immediately
- Clean your list -- remove contacts who haven't engaged in 90+ days
- Avoid spam triggers -- no ALL CAPS subjects, excessive exclamation marks, or misleading content
- Unsubscribe link -- required by CAN-SPAM and GDPR on commercial email. Synapse adds this automatically; see CAN-SPAM Compliance
CAN-SPAM Compliance
Synapse handles CAN-SPAM compliance for your commercial email automatically. You don't add a footer or an unsubscribe link yourself — Synapse injects them at send time.
What gets added to commercial email
Every commercial email (campaigns, promotional flow steps, and promotional direct sends) automatically carries:
- Your physical mailing address, appended to the bottom of the email.
- An unsubscribe link, plus one-click unsubscribe support in Gmail, Yahoo, and Apple Mail (see One-Click Unsubscribe).
Transactional email — password resets, receipts, verification codes — is exempt. It carries no footer and no unsubscribe link, because it isn't marketing.
You must complete your company address first
Your workspace must have a complete company address before you can send commercial email. If it doesn't, commercial sends are blocked — the email is not delivered and is logged as suppressed. This is deliberate: a commercial email without a physical mailing address is itself a CAN-SPAM violation, so Synapse refuses to send it rather than send something non-compliant.
Add your company's legal name and physical mailing address in Settings > General. The required fields are company name, address line 1, city, postal code, and country. This is the same company information required to go live — completing it once satisfies both.
Transactional email is never blocked by this check.
One-Click Unsubscribe
Commercial email includes the List-Unsubscribe and List-Unsubscribe-Post headers that Gmail, Yahoo, and Apple Mail require from bulk senders. Recipients can unsubscribe with a single click directly from their inbox, without opening the email. When they do, the contact is unsubscribed from all commercial email in your workspace and future commercial sends to them are suppressed. Transactional email still reaches them.
The unsubscribe link in the footer and the one-click header both point at a hosted unsubscribe page — you don't host or handle anything. Developers can read more in the Unsubscribe API reference.
Email Logs
Every email sent through Synapse is logged with delivery status. View email logs in Settings > Email Logs or via the Email Logs API.
Log entries include:
- Recipient email and contact ID
- Template used
- Delivery status (sent, delivered, bounced, failed, opened, clicked)
- Timestamps for each status change
- Error details for failed deliveries
Suppression List
Synapse automatically stops sending to contacts based on delivery and consent signals. The scope of the block depends on the signal:
- Hard bounced (invalid email address) — blocked from all email. Continuing to send damages your sender reputation.
- Reported spam — blocked from all email.
- Unsubscribed — blocked from commercial email only. Transactional messages (password resets, receipts, verification codes) still reach them, because an unsubscribe is an opt-out of marketing, not of service messages.
All suppression events are logged. You can view and manage the suppression list in Settings > Email Logs.