The worst time to discover your emails go to spam is after you have sent to your whole list. First campaigns fail for predictable, fixable reasons, almost all of them set up before you write a single subject line. This is a pre-flight checklist: eight checks to run before you send, in the order that catches problems earliest. You can verify most of them in one pass with the Domain Health Report instead of testing them one message at a time.
1. SPF exists and covers your actual sender
SPF lists which servers are allowed to send mail as your domain. The failure that sinks first campaigns is sending through a new tool (Mailchimp, your CRM, a transactional service) whose servers are not in your SPF record. The receiving server sees mail claiming to be you from a server you never authorized, and treats it as suspicious.
Check: confirm you have exactly one SPF record and that it includes the sending service you are about to use. One record only; multiple SPF records is itself a failure. The SPF checker shows the record that is live and flags a duplicate.
2. SPF stays under the 10-lookup limit
SPF has a hard limit of 10 DNS lookups per evaluation. Every "include" for a mail service counts, and they nest. Stack a few services and you blow past 10, at which point SPF returns a permerror and receivers may ignore it entirely.
Check: count your lookups. If you are near the limit, flatten or consolidate before you add another sender. The SPF checker reports the lookup count so you know how much headroom is left.
3. DKIM is set up and signing
DKIM adds a cryptographic signature to each message so the receiver can confirm it really came from you and was not altered. It is the single strongest signal that you are a legitimate sender. Sending your first campaign with no DKIM is a common, avoidable mistake, because most sending platforms give you the DKIM record to publish and people skip that step.
Check: confirm your sending platform's DKIM record is published in your DNS and that test messages show a passing DKIM signature.
4. DMARC is published (start at monitoring)
DMARC ties SPF and DKIM together and tells receivers what to do with mail that fails both. Just as important, it gives you reports on who is sending as your domain. For a first campaign, publish a DMARC record set to monitoring so you get visibility without risking your own mail.
Check: confirm a DMARC record exists. If this is genuinely your first send, keep the policy at monitor-only until you have confirmed your legitimate mail passes, then tighten later.
5. SPF and DKIM alignment with your From domain
Passing SPF and DKIM is not enough for DMARC; the domains have to align with the domain in your visible From address. A frequent trap: your platform passes SPF and DKIM on its own domain, but your From address is your brand domain, and they do not align, so DMARC still fails.
Check: make sure the domain that passes DKIM matches your From domain, which usually means completing the platform's custom-domain (branded sending) setup rather than sending from their shared domain.
6. Your sending domain has forward and reverse DNS in order
Receivers check that the sending IP has a valid PTR (reverse DNS) record and that it matches forward DNS. If you send through a reputable platform this is handled for you, but if you are sending from your own server, missing or mismatched reverse DNS is an instant strike against you.
Check: if using your own mail server, confirm the IP has a PTR record that resolves back to a matching hostname. On a shared platform, this is the platform's job, but it is worth knowing why a self-hosted send can fail.
7. Your domain and IP are not on a blocklist
Even a perfectly configured domain lands in spam if it or its sending IP is listed on a major blocklist, which can happen to a new domain or a recycled IP. Check before you send, not after your open rate craters.
Check: verify your domain and sending IP against the common blocklists. If you are on one, resolve the listing before the campaign, since a listed sender is filtered regardless of how clean your DNS is.
8. Your domain is warm enough for the volume
A brand-new domain with zero sending history that suddenly blasts thousands of emails looks exactly like a spam operation to receivers. Reputation is built gradually. If your domain is new, warm it up by sending smaller volumes first and growing over days, rather than making the first send your largest.
Check: if the domain is new, plan a ramp instead of a single large blast. Send to your most engaged contacts first, since early opens and replies build reputation that carries the later, larger sends.
Run the pre-flight in one pass
Checks 1 through 5, plus the blocklist and reverse-DNS items, are all things a DNS and mail scan reads directly. Before you schedule the campaign, run the Domain Health Report once and clear every mail-related flag it raises. Fix SPF, DKIM, and alignment first, confirm you are off the blocklists, then send a small test batch to seed accounts across a few providers to confirm inbox placement. Do the pre-flight and your first campaign lands where you sent it, instead of teaching you these lessons the expensive way.