What email deliverability is
Email deliverability is the chance that a message a server accepted also lands in the inbox. Email delivery rate is the earlier number: the share of attempts the receiving server agreed to take. A bounce is a refusal, so it never becomes an inbox placement.
People search “email delivery best practices” and “email deliverability best practices” for the same checklist. The words split the job in two. Delivery is acceptance. Deliverability is placement. You can have a high delivery rate and a wrecked inbox, because spam-folder mail was accepted.
Deliverability
Accepted mail that reaches the inbox. Complaints, volume spikes, and a domain the receiver does not trust move this number.
Delivery rate
Attempts the receiving server accepted. Dead addresses and blocked domains pull this down. Spam placement does not.
Bounce rate
Attempts the server refused. The formula, the 2% line, and the hard-versus-soft split are on Email bounce rate.
The eight practices below are the order that keeps both numbers intact. Authentication tells the receiver who you are. The list tells them you are writing to real people. Volume, permission, and unsubscribe behavior tell them you behave like a sender they can keep accepting.
1. Authenticate the domain
SPF, DKIM, and DMARC are how a receiver checks that the message came from a domain allowed to send it. SPF names the servers that may send for the domain. DKIM signs the message so it cannot be quietly altered. DMARC tells the receiver what to do when SPF or DKIM fails, and it requires the visible From domain to line up with the domain that authenticated.
Google's email sender guidelines expect bulk senders to authenticate with SPF and DKIM, and to publish DMARC. A From address on a domain you do not control, or a signature on a different domain than the one in the From line, fails that check before the words in the email matter.
Alignment is the part people skip. The domain in the visible From line has to match the domain that passed SPF or DKIM. A sending platform that signs with its own domain, while the From line shows yours, fails that check even when both records exist. Set a custom DKIM domain on the platform so the signature uses the same domain the reader sees.
Set the records on the domain you actually send from. A new outreach domain needs its own SPF, DKIM, and DMARC. Borrowing the company domain's records for a lookalike hostname does not authenticate the hostname in the From line. After the records are live, send a message to an account you control and confirm the headers show SPF pass, DKIM pass, and a From domain that matches.
2. Verify the list before the send
A formatted address is not a mailbox. [email protected] can pass a syntax check and still not exist. Verification asks the receiving server whether that recipient can take mail. It does not deliver a message, and the inbox owner is not notified.
Do this before the first send on a new file, and again before you mail a segment that has been sitting. Job changes, closed accounts, and typos accumulate in a CRM even when the original signup was real. A cheap check that returns "unknown" on Yahoo, AOL, or Outlook leaves those rows in the file, and the campaign bounces them later. That pattern is why the bounce-rate guide says to read the provider, not only the total.
A syntax check belongs earlier, when the form rejects a missing @ or a space. It is not this step. This step is the mailbox. Remove invalid and hard-bounce rows before the export reaches the sending tool. Keep unknown rows out of the first send on a new domain, and review them instead of treating "unknown" as safe.
Try the check on one Gmail address with the free Gmail checker. Gmail is the easy row. A CSV that mixes providers is the paid run. The 16-address list and the scoring rules are on How we test. New accounts start with 100 verifications.
3. Keep the bounce rate under 2%
Under 2% is the operating line for a permission list. From 2% to 5%, the file is drifting and the next send should wait on a verification pass. Above 5%, stop, remove every hard bounce, and resume only after a fresh check is back under 2%.
Suppress a hard bounce after one failure, in the sending tool and in the CRM. The next sequence will mail it again if you leave it in either place. The formula, hard versus soft, the calculator, and the full fix order stay on Email bounce rate. Cold outbound runs into more job changes than a newsletter. The 2% ceiling still applies.
Google's sender guidelines say that when messages start bouncing or being deferred, cut volume until the error rate falls, then increase slowly. A bounce report still cannot see spam-folder placement. That is the next practice.
4. Stay under Google's complaint line
A complaint is a person marking the message as spam. The server already accepted it, so it never shows up in the bounce rate. A list can look clean at 0.4% bounces and still be over the complaint line.
Google's sender guidelines tell bulk senders to keep the Postmaster Tools spam rate under 0.10%, and to avoid ever reaching 0.30%. That is the number to watch after the send. A 0.4% bounce rate with a 0.4% complaint rate is still over that 0.30% line. The bounce report cannot see it.
Complaints come from mail people did not ask for, mail they no longer want, and mail that is hard to refuse. The next three practices are how you keep that rate down. Verification removes dead addresses. It does not remove a person who signed up two years ago and now hits "spam" instead of unsubscribe.
5. Raise volume slowly
A new domain has no history. A domain that suddenly sends ten times its usual volume looks like a compromised account, even when the list is real. Receivers defer or soft-bounce that mail, and the bounce rate climbs for a reason a verification pass will not fix.
Start on the new domain with the people most likely to accept the mail: recent signups, recent repliers, people who opened or clicked. Widen only after that slice stays under the 2% bounce line and complaints stay under Google's 0.10% line. If the small slice already bounces, the file is the problem and more volume makes it worse.
When bounces or deferrals start on a domain that was fine, Google's guidance is to cut volume until the error rate falls, then increase slowly. Keep a steady cadence. A quiet domain that wakes up with a full database is the same shape as a brand-new domain.
Warm the reputation with mail people asked for. Widen only while the bounce rate on that slice stays under 2% and complaints stay under Google's 0.10% line. A warmup network that only exchanges automated messages with other warmup tools does not prove that your list wants to hear from you.
6. Mail people who asked
Google's sender guidelines say to confirm each recipient before you subscribe them, and not to buy addresses. A purchased list, a scraped list, and an old event scan are bounce-rate problems you paid for. Double opt-in, or a live check on the signup form, stops the typo before it joins the file.
Permission also expires in practice. Someone who has not opened or clicked across a long stretch of sends is the person most likely to mark the next one as spam. Retire that address, or ask them to confirm they still want the mail, before you keep sending. A re-permission note to the engaged slice is a send. A re-permission note to the entire dormant file is a complaint spike.
Role addresses such as info@ and sales@, and catch-all company domains, need a separate look. A catch-all server accepts every address at the domain, then drops or bounces later, so the first report looks clean. The bounce-rate page explains that limit. Verification can still remove the addresses that are clearly dead. It cannot turn a catch-all domain into a list of confirmed people.
7. Make unsubscribe obvious
People who cannot find unsubscribe use the spam button. That complaint hits the 0.10% line. The unsubscribe link belongs where they look for it, and it has to work without a login or a survey.
Google's sender guidelines require one-click unsubscribe for bulk senders, and they tell you to honor it within two days. Process the request in the sending tool and in the CRM. An unsubscribe that only stops one campaign leaves the address in the next sequence, and the next complaint is earned.
The same rule covers the people whose mail keeps bouncing. Google's guidelines allow you to unsubscribe addresses that repeatedly fail. Leaving them in the file protects no one. It trains the receiver that you mail mailboxes that do not exist.
8. Read reputation after the send
The campaign report shows accepts and refusals. Postmaster Tools, or your provider's equivalent, shows complaints, authentication, and reputation. Use both. A clean bounce rate with a rising spam rate means the mail is being accepted and then rejected by the person, which is a permission problem. A rising bounce rate with quiet complaints means the file or the volume is the problem.
Check SPF, DKIM, and DMARC on a real message after any DNS change. A record that looked right in the editor and fails in the header is a failed practice, whatever the checklist says. If authentication passes and mail still lands in spam, go back to the list, the complaint rate, and the volume. A dedicated IP does not repair a dirty file. A shared IP can add someone else's reputation on top of yours. Either way, the first fix is the list and the send pattern, then the infrastructure.
When the next file is ready, verify it before it goes out. The Gmail row is free on the Gmail checker. The rest of the providers are the bulk check described on How we test.