Most agency deliverability problems do not arrive as emergencies. They arrive as gradual drift. A client’s Yahoo inbox rate quietly falls from 91% to 74% over six weeks. A complaint rate that was 0.05% in January is 0.09% in March. A DKIM pass rate that used to be 100% is now 96% because someone added a new transactional email tool without updating DNS. None of these trigger an alert in Klaviyo. All of them compound if nobody checks.
According to Validity’s 2024 State of Email report, only 20% of marketing teams have a formal process for monitoring deliverability on a recurring cadence. For agencies managing multiple clients simultaneously, that gap is even more pronounced: the accounts that get reviewed are the ones with active problems, not the ones quietly drifting toward one.
The agencies that maintain strong deliverability across a roster of eCommerce clients are not doing more complex work. They are doing a structured review on a consistent cadence. Here is what that review covers and why each piece matters.
Why Monthly Is the Right Cadence
Weekly monitoring of every client is not practical for most agencies. Checking only when something breaks means you are always in recovery mode. Monthly sits in the right middle: frequent enough to catch gradual drift before it compounds, infrequent enough to be operationally sustainable.
The exception: clients who are actively recovering from a deliverability problem, running a major list import, or approaching a high-volume period like BFCM. Those clients warrant weekly checks on complaint rate and inbox placement until they are stable.
For everyone else, a structured monthly review takes fifteen to twenty minutes per client once the process is established. The time investment is negligible compared to the time cost of managing a complaint rate crisis or a blacklist removal.
Authentication Compliance Checklist
Authentication is the foundation everything else builds on. It also drifts. New sending tools get added, DNS records get edited by someone on the client’s IT team, ESP migrations leave old SPF includes in place. A configuration that was clean in January may not be clean in June.
What to check:
DKIM pass rate at 100%. Google Postmaster Tools shows DKIM pass rate under Authentication. Any number below 100% means at least one sending source is signing mail with a key that does not align with the sending domain, or is not signing at all. Even a 96% DKIM pass rate means roughly 4 in 100 sends are not building domain reputation correctly. Track down the sending source and fix the configuration.
DMARC policy at quarantine or reject. If a client is still on p=none, they are not enforcing and they are not meeting the bulk sender requirements that Gmail and Yahoo introduced in 2024. Move to p=quarantine once you have confirmed all legitimate sending sources are passing. The SPF, DKIM, and DMARC guide covers the full progression.
SPF includes all current sending sources. Run a quick SPF lookup for the client’s sending domain and verify the record matches reality. If they have added a transactional email provider, a helpdesk tool with email notifications, or any other sending source in the past 30 days, the SPF record needs updating. An SPF record that does not include a current sending source causes that source’s mail to fail authentication.
DMARC alignment passing. The From domain, DKIM signing domain, and Return-Path domain need to align. To verify, send a test email to a Gmail address and open the original message headers. Look for the Authentication-Results header: it should show dkim=pass with a d= value that matches the From domain, and dmarc=pass. Misalignment shows as a DMARC pass on the record-level check but a DMARC fail or dmarc=bestguesspass in actual mail headers, which does not build brand-level domain reputation correctly. MXToolbox’s DMARC lookup also surfaces alignment configuration issues without requiring a test send.
InboxEagle’s authentication monitoring surfaces DKIM pass rate and DMARC alignment status per client domain in a single view, which removes the need to log into Postmaster Tools per client to pull the same check each month.
Flag any client where DKIM pass rate is below 100% or DMARC is at p=none as a priority item for the current month.
Inbox Placement Checklist
Delivery rate, the percentage of emails accepted by the receiving server, is what Klaviyo surfaces prominently. It is not the number that tells you whether subscribers are seeing the client’s emails. Inbox placement rate is.
The critical distinction: a client with 99.2% delivery rate can have a 58% inbox placement rate at Gmail if their domain reputation has degraded enough for Gmail to route the majority of delivered mail to Promotions or spam. That gap is invisible in the Klaviyo dashboard.
What to check:
Inbox placement at Gmail, Yahoo, and Outlook, broken down separately. Each provider filters differently. A client whose Gmail inbox rate is stable but whose Yahoo inbox rate has dropped 15 points over three months has a list quality signal that Yahoo is catching before Gmail does. Yahoo responds to engagement signals faster, which makes it the leading indicator. If Yahoo is declining, Gmail often follows four to eight weeks later.
Promotions tab rate at Gmail. A rising Promotions rate is not the same as spam, but it is a precursor signal. Gmail routes mail to Promotions when domain reputation is moderate and engagement signals are mixed. A Promotions rate climbing past 25% to 30% is worth addressing before it becomes a spam placement problem.
Campaign-level placement variation. If one campaign in the month had significantly worse placement than the others, that campaign is the data point to investigate. What was different about the audience segment, the content, or the send timing? Campaign-level placement data is what separates a useful review from a high-level numbers exercise.
InboxEagle’s placement monitoring gives this breakdown per campaign per client without requiring manual seed list runs for each send. For agencies managing more than four or five clients, per-campaign placement data at this level is what makes the monthly review operationally feasible.
One view across all your clients
Agency placement monitoring without the manual work.
Per-campaign inbox placement at Gmail, Yahoo, and Outlook for every client. Catch the drift before it compounds.
Complaint Rate Checklist
Complaint rate is the metric most closely correlated with short-term inbox placement changes. A complaint rate above 0.10% at Gmail triggers filtering consequences. Above 0.30% triggers more severe action. Yahoo’s thresholds are similar.
Google Postmaster Tools shows complaint rate per day for each domain. The number reported is based on Gmail feedback loop data, which underrepresents actual complaint volume because Gmail only reports a sample. A complaint rate of 0.09% in Postmaster Tools should be treated with the same urgency as 0.10%, not as safely under the threshold.
What to check:
Complaint rate trend over the past 30 days. A rate that was flat at 0.03% for three months and is now trending toward 0.07% is more concerning than a rate holding steady at 0.06%. Trend matters as much as absolute level.
Complaint rate spikes tied to specific sends. Postmaster Tools shows complaint rate by day. Cross-reference any spike against the client’s send calendar. A spike on a specific date that matches a campaign send identifies which audience and which content to investigate.
Whether any single flow or campaign is the driver. In Klaviyo, complaint data is not surfaced natively at the campaign level. If the Postmaster Tools data shows elevated complaint rates but the aggregate looks acceptable, check whether a specific automated flow is responsible. Win-back flows and re-engagement campaigns are the most common source of complaint rate problems in otherwise well-managed accounts.
Any client with a complaint rate above 0.08% gets a suppression and frequency review before their next high-volume send.
Bounce Rate and List Health Checklist
Hard bounces are the most direct signal of list quality problems, and they compound if not addressed. A hard bounce rate above 2% on a single send is a significant list quality problem. A bounce rate consistently above 0.5% across consecutive sends indicates ongoing collection or suppression issues.
What to check:
Hard bounce rate per campaign over the past 30 days. Klaviyo suppresses hard bounces automatically, but the suppression only applies going forward. If a client is importing contacts from external sources, re-importing suppressed contacts, or collecting addresses through checkout flows with no validation, hard bounces will keep appearing.
Whether suppressed addresses are being re-introduced. This happens most often during CRM migrations, platform switches, or when a client’s e-commerce platform syncs contacts back to Klaviyo without respecting the suppression list. Check the suppression list size in Klaviyo for any client who recently migrated platforms or ran a bulk import.
Net list growth versus gross growth. A list that grew by 800 subscribers but added 600 to suppressions in the same month is not growing meaningfully. The suppression growth signals an underlying collection or list quality problem worth investigating.
Unengaged profile accumulation. Check the size of the segment that has not opened or clicked in the past 90 days. For high-frequency senders, this segment should be excluded from campaigns and reviewed monthly. If it is growing faster than the engaged segment, the list quality trend is moving in the wrong direction.
The email list hygiene guide covers the Klaviyo segment builds for engagement-based suppression if a client does not have them in place.
Blacklist Status Checklist
Most blacklist incidents are detectable before they cause visible inbox placement problems. A listing on a minor blacklist does not immediately affect Gmail or Yahoo inbox rates, but it is a signal that something is wrong and should be investigated before it escalates.
What to check:
Sending domain and IP against major blacklists. Run the client’s sending subdomain and sending IP through a blacklist checker monthly. The major lists to flag: Spamhaus DBL (domain), Spamhaus SBL (IP), Barracuda, and Microsoft SNDS for Outlook-specific IP reputation.
Microsoft SNDS for Outlook placement. Microsoft’s Smart Network Data Services tool provides IP-level data for Outlook deliverability that Postmaster Tools does not cover. Outlook placement problems often show up in SNDS data before they are obvious in campaign open rates. For clients with significant Outlook audiences, SNDS is worth checking monthly.
Any new listings since last month. A client who was clean last month and has a new listing this month has had a reputation event in the intervening period. The listing is the symptom. The cause is in the complaint rate data, bounce data, or send behavior from the past 30 days.
InboxEagle flags blacklist listings per client domain as part of its deliverability monitoring, so agencies do not need to run manual checks across each client’s sending domain and IP separately. The email blacklist check and removal guide covers the removal process for each major operator if a listing does appear.
Putting It Into a Repeatable Process
The monthly review works as a structured process only if it is documented and assigned. An informal check that depends on someone remembering to look is not a process. It is a recurring fire drill waiting to happen.
For each client, the review should produce:
- A status flag for each section: green (no action needed), yellow (monitoring), or red (action required this month)
- A documented action item for every red and yellow flag, with an owner and a due date
- A brief summary to share with the client that translates the numbers into plain language
The summary does not need to be a full report every month. For clients in green across all sections, a one-paragraph note confirming status and any notable numbers is sufficient. The full report format is worth saving for quarterly reviews or when something notable happened during the month.
For agencies managing more than five clients, the operational constraint is not the review itself but the data collection. Pulling inbox placement data per campaign per client manually is the part that does not scale. Centralizing placement monitoring across clients is what makes the monthly cadence sustainable rather than aspirational. The agency deliverability management guide covers the infrastructure layer: domain isolation, monitoring setup, and the mistakes that let one client’s problems affect another’s.
Note: Content created with the help of AI and human-edited and fact-checked to avoid AI hallucinations.
