Table of contents
- The 11 essential metrics and what they mean
- Delivery rate
- Open rate
- Click-through rate (CTR)
- Reply rate
- Spam complaints
- Bounces (Hard)
- Bounces (Soft)
- Summary and benchmark table
- Frequently asked questions
The 11 essential metrics and what they mean
Before judging whether a metric is "good", it is essential to understand exactly what it measures. Here are the most common metrics you will come across when analysing your email campaigns.
Processed
The total number of message requests received by the sending server, both outbound and inbound.
Accepted
The total number of outbound message requests accepted for sending (the emails you attempted to send).
Delivered
The total number of requested messages that were actually delivered to the recipient's mail server.
Opens
The total number of times a delivered email recorded an open (this does not necessarily mean a person read it).
Clicks
The total number of times a delivered email recorded a click on a link.
Replies
The total number of times a delivered email received a reply from the recipient.
Bounces (Hard)
Accepted messages that could not be delivered because of incorrect addresses or inactive accounts. Often described as a "permanent failure".
Bounces (Soft)
A temporary delivery failure. The system automatically tries to send the email again. During the retries, the email shows the status Sent and the details show Delivery in progress.
Spam complaints
Delivered emails that the recipient marks as spam or junk mail.
Unsubscribes
Delivered emails that led the recipient to click the unsubscribe link.
Suppressions
Accepted messages that were not delivered because the address had previously generated a bounce, a spam complaint or an unsubscribe.
Delivery rate
Optimal: 98% or higher
Warning: Between 97% and 98%
Alert: Below 97%
It is important to monitor the delivery rate both at domain level and for every individual email campaign.
A delivery rate below 97% usually means that most delivered emails are landing in the spam or promotions folders. A low delivery rate is often a symptom of multiple problems (reputation, authentication, list quality), not of a single factor.
Open rate
Optimal: 40–60% or higher
Average: 16–26%
Alert: Below 15%
The open rate should be monitored at individual email campaign level. To improve it, optimise everything a recipient sees before opening: sender name, email address, subject line and preview text.
The decision to open an email is also based on trust. Present yourself in a way that feels familiar and trustworthy to your contacts.
Watch out for iOS 15+
Apple's "Mail Privacy Protection" feature automatically triggers opens for many users, even when the email is not read. If a significant share of your list uses Apple Mail, analyse the open rate alongside clicks and replies.
Click-through rate (CTR)
Optimal: Above 10%
Average: 7–9%
Alert: Below 5%
Monitor the click-through rate at individual email campaign level, above all when the main goal is to get a click on your call to action (CTA).
Make your CTA clear and simple. Explain exactly what recipients will get by clicking. Avoid adding too many links that could distract from the main action you want.
Reply rate
Optimal: 30% or higher
Average: 15–25%
Alert: Below 10%
Check the reply rate at individual email campaign level, especially when your main CTA is a request for a reply.
To encourage replies, ask simple (yes/no) questions or offer something of value in return. Avoid adding clickable links that could pull attention away from the request for a reply.
Spam complaints
Optimal: As close as possible to 0.00%
AUP threshold: 0.05%
Alert: 0.04% or higher
The maximum threshold in the acceptable use policy (AUP) is 0.05%, which is roughly 1 complaint for every 2,000 emails. If you get close to this limit, your domain reputation is already at risk.
Monitor this figure both at domain level and for the individual campaign. High complaint rates can lead to your domain or account being suspended and can get you blacklisted.
Bounces (Hard)
Optimal: Well below 1%
AUP threshold: 5%
Alert: Above 2–2.5%
Monitor the bounce rate at domain level and for the individual campaign. Proper list hygiene (initial and ongoing) should keep this value very low.
When the hard bounce rate approaches 2-2.5%, your domain and IP reputation start to suffer. High rates can lead to your account being suspended.
Bounces (Soft)
Optimal: Below 2%
Warning: 2–5%
Alert: Above 5%
Unlike hard bounces (which are permanent), soft bounces are temporary. Common causes include a full mailbox, a temporarily unavailable server or a message that is too large.
The system retries delivery automatically. If you notice that an address bounces softly again and again, treat it as a hard bounce and remove it from your active list.
Do not mistake "Delivery in progress" for a problem
Seeing the status "Delivery in progress" in the email details does not mean there is an error. It simply indicates that the system is still trying to deliver the email after a soft bounce. Wait for the status to resolve to "Delivered" or "Failed".
Summary and benchmark table
These numbers are guidelines, not absolute rules. Results depend on the type of campaign, the audience and the message. Monitor your metrics weekly so you can correct course in time.
| Metric | Optimal | Warning | Alert |
|---|---|---|---|
| Delivered | ≥ 98% | 97–98% | < 97% |
| Opens | 40–60%+ | 16–26% | < 15% |
| Clicks | > 10% | 7–9% | < 5% |
| Replies | 30%+ | 15–25% | < 10% |
| Spam complaints | ≈ 0.00% | < 0.04% | ≥ 0.04% |
| Bounces (Hard) | < 1% | 1–2% | > 2–2.5% |
| Bounces (Soft) | < 2% | 2–5% | > 5% |
The goal is not to hit a specific number, but to improve steadily from your starting point. Analyse your current data, set targets and make one small change at a time so you can measure its effect.
Frequently asked questions
Which metric is the most important to monitor?
The spam complaint rate, followed closely by the bounce rate. Both damage your sender reputation directly and quickly, and can lead to account-level action from your SMTP provider.
What does "Delivery in progress" mean in the email details?
It means the email hit a soft bounce and the system is actively trying to deliver it again. It is not a failure status, but an in-progress one. There is no need to send the email again manually.
What is the difference between a Hard Bounce and a Soft Bounce?
A Hard Bounce is a permanent failure (address does not exist, account closed). A Soft Bounce is a temporary failure (full mailbox, server unavailable). If an address bounces softly again and again, treat it as a hard bounce.
Why has my open rate been so unstable since iOS 15?
Apple's "Mail Privacy Protection" feature pre-loads images, triggering opens automatically. If a large part of your audience uses Apple Mail, your open rate is inflated. Assess it alongside click and reply rates.
Is a low delivery rate always a reputation problem?
Not always. Sometimes it comes down to list quality (incorrect addresses, spam traps) or authentication issues (SPF, DKIM, DMARC). That said, a chronically low delivery rate is almost always a combination of several problems.
What is the difference between Accepted and Delivered?
Accepted means the system received your send request. Delivered means the recipient's mail server accepted the email. The gap between the two figures is made up of bounces, rejections and suppressions.
Unsubscribe or spam complaint: which is worse?
Spam complaints are far worse. Unsubscribes do not damage your reputation, they simply remove a contact who is not interested. Complaints tell providers that your emails are unwanted and carry enormous weight on reputation.
How often should I monitor these metrics?
At least weekly. That is frequent enough to spot problems before they damage your reputation, but not so frequent that every normal fluctuation looks like a crisis. Track trends, not individual data points.
My campaign has crossed the "Alert" thresholds: what do I do now?
Pause any further sends to that list, aggressively clean out the contacts that generated bounces and complaints, and check your authentication records. Reduce your sending volume and start again by mailing only the most engaged segment of your list before scaling volumes back up.