Fixing deliverability errors
What each DNS/SMTP error actually means, and how to fix it.
Two places things break
Deliverability problems in Sumezi show up in two places: an SMTP send that fails outright (from Settings, SMTP, or from a real campaign send), and a DNS/domain status that stays unverified (from Settings, Deliverability). This page covers both — for adding your SPF, DKIM and DMARC records from scratch, see "Verify your own sending domain" instead.
SMTP send errors
These are the exact messages Sumezi surfaces when a test mail or a campaign send fails — Sumezi passes through the underlying mail library's error rather than rewording it, so you can match it directly against the table below.
| Error message | Likely cause | Fix |
|---|---|---|
| SMTP Error: Could not connect to SMTP host. | Wrong host or port, the connection is blocked, or STARTTLS negotiation failed | Double-check Host and Port against your provider's docs, and match Encryption to the port (587+STARTTLS or 465+SSL/TLS) |
| SMTP Error: Could not authenticate. | Wrong username/password, or the provider requires an app-specific password | Re-enter Username and Password; for Gmail, Microsoft 365 and similar with 2FA, use an app-specific password |
| The following From address failed: ... | The provider rejected your From email, often because it isn't verified for the account you authenticated with | Set From email to an address that belongs to (or is verified under) that account |
| SMTP Error: The following recipients failed: ... | The receiving server rejected the recipient address | Check the exact address you're sending to; if it's your own address, confirm it's a real mailbox |
| SMTP Error: data not accepted. | The server accepted the connection and recipient but rejected the message itself | Rare — check with your provider for content or size restrictions |
| SMTP is not configured for this project. | Host is empty — SMTP was never saved | Fill in and save Host, Port, Username and Password on the SMTP page |
| The saved SMTP password could not be read on the server… | An internal encryption issue on Sumezi's side | Re-enter your SMTP password (even if unchanged) and save again |
Domain verification statuses
Under Settings, Deliverability, Sumezi checks SPF, DKIM and DMARC for the domain of your From email address and shows one of three states per record:
- Not checked (grey): no check has run yet, or the record type hasn't been looked up.
- Verified (green): a live DNS lookup found a matching record right now.
- Not found (amber): the lookup didn't find the expected record — this also covers a lookup that simply failed to resolve, so it doesn't always mean the record itself is wrong.
Locked instead of status pills? Domain verification (SPF/DKIM/DMARC status checks) requires the Starter plan or higher. On the Free plan, Settings, Deliverability shows an upgrade prompt instead of live statuses — upgrading unlocks the checks immediately.
Common misconfigurations
If a record shows Not found and you're confident you added it correctly, these are the usual culprits:
- Just added it: DNS changes can take up to 24 hours to propagate. Wait and click "Re-verify" again later rather than re-editing the record.
- Wrong host value: a trailing dot, an extra copy of your domain, or the record placed under www. instead of the root will all cause a mismatch — compare the host value character for character with what Sumezi shows you.
- Duplicate SPF: a domain can only have one record starting with v=spf1. If you already had one before adding Sumezi's, merge them into a single TXT record instead of creating a second one.
- DKIM never verifies: DKIM resolves through a CNAME chain — double-check the selector/host name is exact (no domain appended twice) and that the CNAME target itself still resolves.
- DMARC not found: the record must sit at _dmarc.yourdomain.com, not at the root, and its value must start with v=DMARC1.