Bounce rate and Spam complaints
Bounces and spam complaints are the two metrics that most directly affect your sender reputation and deliverability. This article explains how they work, what the different bounce types and codes mean, what to do when numbers are high, and how to prevent problems before they happen.
In this article
Bounce rate
While your delivery rate measures the emails that reached the receiving server, your bounce rate measures the opposite — the percentage of sent emails that were rejected by the receiving server and never reached the recipient.
All Email Reports contain bounce information. To see which Profiles bounced and their corresponding bounce code and reason, go to the Bounces tab of the Email Report and click Export to download the full list.
Bounce types and codes
Email bounces are divided into three categories: soft, hard, and technical. Each type has specific bounce codes that tell you exactly what went wrong.
Soft bounces
A soft bounce is caused by a temporary issue. Apsis One retries delivery every hour for up to 48 hours after the initial send time. If the email still can't be delivered after 48 hours, no further action is taken.
Code | Reason |
3001 | Soft – Mailbox is full |
3002 | Soft – Recipient email server is currently too busy |
3003 | Soft – Email account is inactive |
4000 | Soft – General error |
4004 | Other – Unknown |
9999 | Soft – Unknown. A catch-all code used when the receiving server rejected or deferred the message with a reason that doesn't map to a more specific bounce category. Common real-world causes include temporary server-side issues (timeout, rate limiting, greylisting), ambiguous or non-standard SMTP error responses, or content-level filtering with a vague rejection. Since it's classified as a soft bounce, Apsis One retries delivery as normal. |
Hard bounces
A hard bounce is a permanent failure — the email could not be delivered and there's no point retrying. Hard bounces are the ones to watch out for.
Once a hard bounce happens, Apsis One won't make more attempts to deliver to that Profile within the same email activity. If a hard bounce happens three (3) times for the same Profile (across any sendings), Apsis One stops sending emails to that Profile altogether. The Profile's consent is not removed — they are simply excluded from future sends.
Note: SMS bounces are treated the same way in Apsis One.
Code | Reason |
1004 | Hard – Unknown |
2000 | Hard – General hard bounce |
2001 | Hard – Recipient email does not exist |
2002 | Hard – Domain name does not exist |
2004 | Hard – Closed email account |
Technical bounces
A technical bounce occurs when the receiving server rejects the email due to a technical error — such as a network issue or an authentication failure (SPF, DKIM, or DMARC).
Apsis One treats technical bounces the same as soft bounces: it retries delivery every hour for up to 48 hours. If the email is still not delivered, the Profile is not affected and will be included in future sendings.
However, if you see a large number of technical bounces, this is a warning sign — it may indicate a problem with your email authentication setup. Contact Customer Service to investigate.
Code | Reason |
4000 | Technical – General error |
4003 | Technical – Network error |
4007 | Technical – SPF authentication error |
4008 | Technical – DMARC authentication error |
4009 | Technical – DKIM authentication error |
What to do about a high bounce rate
Monitor your bounce rate in the Email Report after every sending — check periodically over 2–3 days as bounces continue to come in.
A bounce rate below 5% is considered normal. As long as you're actively taking steps to prevent bounces, there's no need to worry.
Bounce rate | What it means | What to do |
Below 5% | Normal range. Your list is in reasonable shape. | Continue regular list hygiene. Monitor trends — is the rate going up or staying stable? |
5% or higher | A concern. Something in your list or process needs attention. | Review the Email Reports from your last few sends. Look at the bounce codes — are they mostly hard bounces (bad addresses) or technical bounces (authentication issues)? Follow the prevention steps below. |
10% or higher | A bad sending. There's likely a serious problem with your email addresses or authentication setup. | Contact Customer Service immediately. Don't send another campaign until the issue is identified and resolved. |
How to prevent bounces
Action | How it helps |
Clean up inactive Profiles | Identify inactive Profiles and unsubscribe or delete them. Create a Segment for inactive Profiles and exclude them from sendings. You can also export matched Profiles and unsubscribe or delete them via the File Import Wizard. |
Re-engage inactive Profiles first | Before removing inactive Profiles, try a re-engagement campaign (e.g. a Marketing Automation flow). If they don't respond, you can confidently exclude or remove them. |
Enable double opt-in | Require new subscribers to confirm their email address via a confirmation email. This prevents spambot signups, typos, and fake addresses from entering your list. |
Ask Profiles to whitelist you | Include a message in your Welcome emails asking recipients to add your sender address to their contacts or safe senders list. This helps prevent legitimate emails from being incorrectly filtered. |
Monitor bounces and spam complaints after every send | Don't send to Profiles who have bounced, unsubscribed, or reported your emails as spam. Apsis One automatically blocks Profiles after 3 hard bounces, but you should also review and clean up your list proactively. |
Use the File Import carefully | Ensure all imported addresses are real and have provided consent. |
⚠️ Never do this
Do not re-subscribe Profiles who have unsubscribed unless you've received explicit, new consent.
Do not import files with addresses provided by a third party.
Under any circumstance, do not harvest email addresses from websites, buy, or rent email lists. It is very difficult — if not impossible — to prove that these individuals consented to your communications.
This also goes against Apsis's terms of service and will result in serious consequences including server blacklisting and damaged sender reputation.
Spam complaints
A spam complaint is recorded when a recipient clicks "Report spam" or "This is spam" in their email client. The spam complaint count in your Email Report reflects only Profiles who actively reported the email — it does not reflect the total number of emails that ended up in a spam or junk folder.
Emails can land in spam or junk folders for several reasons: previous spam complaints from other recipients, technical issues (missing authentication), or a poor sender reputation. Your sender reputation is directly affected by how consistently you follow deliverability best practices.
💡 Spam complaint visibility is limited
Apsis can only show spam complaints that are sent back via Feedback Loops (FBLs) from email providers. Not all providers participate — notably, Gmail does not send complaints through Feedback Loops. To see spam complaint data for Gmail recipients, you need to set up Google Postmaster Tools for your sending domain. This is a free Google tool that gives you visibility into your domain's reputation and spam rate among Gmail users.
Spam traps
Your sender reputation can be severely damaged by sending to spam traps — email addresses specifically designed to catch spammers. Since spam traps don't belong to a real person, sending to one means you obtained the address without legitimate consent.
There are three types of spam traps:
Type | What it is | What it signals |
Pure spam traps | Created artificially to lure spammers. These addresses have never been associated with a real person. | You're likely using a purchased or harvested list. This is the most damaging type. |
Recycled email addresses | Addresses that once belonged to a real person but were abandoned for so long that the email provider repurposed them as spam traps. | Your list contains outdated addresses. You haven't cleaned up inactive Profiles. |
Invalid email addresses | Addresses with typos (e.g. | Your signup process doesn't validate email addresses. Enable double opt-in to prevent this. |
💡 How to avoid spam traps
You can't identify spam traps by looking at your list — they look like normal email addresses. The best defence is prevention: enable double opt-in for all signups, never import third-party lists, regularly clean inactive Profiles, and monitor bounce rates closely. If you suspect your list contains spam traps (e.g. sudden deliverability drop with no obvious cause), contact Customer Service.
How to prevent spam complaints
As long as you maintain a steady sending schedule, consistent frequency, and good data hygiene, spam complaints should stay low. To minimise risk:
Action | Why it matters |
Set up email authentication | Ensure SPF, DKIM, and DMARC are properly configured. Missing authentication is one of the most common reasons emails are flagged as suspicious. |
Align your team on deliverability practices | Make sure all users in your account understand and follow the guidelines in Keep Deliverability High. One team member importing a bad list can damage the reputation for everyone. |
Make unsubscribing easy - show respect and honor opt-outs. | A visible, easy-to-find unsubscribe link reduces spam complaints. If recipients can't find the opt-out, they hit the spam button instead — which is far more damaging to your reputation. |
Send relevant content | Irrelevant or overly frequent emails cause recipients to disengage or report spam. Use Segmentation to target the right audience with the right message. |
Maintain a consistent sending schedule | Sending irregularly (e.g. nothing for months, then a sudden large campaign) can trigger spam filters and confuse recipients who've forgotten they subscribed. |
Enable double opt-in | Confirms that the subscriber actually owns the email address and wants to receive your communications. Eliminates fake signups, spambot entries, and typos. |
Blacklisting
A blacklist is a list of servers or domains that have been identified as sources of spam. Getting listed on a blacklist can seriously impact your deliverability.
How blacklisting works
Recipient servers check blacklists when receiving an email to determine whether the sender is trustworthy.
The blacklist itself doesn't block your email — it simply provides information about the sender. The recipient server decides what to do.
If the sender is on a blacklist, the recipient server may flag the email (sending it to spam/junk), reject it entirely, or in some cases let it through — depending on the recipient's policies.
Listing duration varies by blacklist — some list senders for just a few hours, others for extended periods.
What Apsis does about blacklisting
The Apsis Delivery team continuously monitors server blacklists and takes action when a listing is detected — identifying the cause, determining why the server was listed, and resolving the issue. All IP addresses are owned and managed by Apsis, so blacklist monitoring and resolution is handled for you.
What you can do
Your deliverability practices directly affect whether your sending infrastructure ends up on a blacklist. As long as you maintain good list hygiene, avoid spam traps, authenticate your emails, and follow the prevention guidelines in this article, blacklisting should not be a concern.
If you suspect a blacklisting issue (e.g. sudden drop in delivery rates across multiple sends), contact Customer Service.
Common questions
Question | Answer |
"A Profile shows both a bounce and a delivery — how is that possible?" | This happens with soft and technical bounces. The first delivery attempt bounced (temporary rejection), but Apsis One retried and a later attempt succeeded. The report records both the bounce event and the delivery event for the same Profile. This is normal — it means the email was eventually delivered. |
"Why does Apsis One allow 3 hard bounces before blocking — why not block after the first one?" | Because not every hard bounce is truly permanent. A receiving server might return a hard bounce code for a temporary reason — for example, a misconfigured server, a missed renewal of the domain name, a brief DNS issue on the recipient's side, or an overly aggressive spam filter that rejects with a permanent error code instead of a temporary one. If Apsis blocked on the first hard bounce, you'd permanently lose the ability to reach Profiles who are actually reachable. The 3-bounce threshold balances protection (you don't keep hammering a genuinely dead address) with accuracy (you don't lose valid recipients over a one-off server hiccup). After 3 hard bounces, it's safe to conclude the address is genuinely undeliverable. |
"My bounce rate suddenly spiked on one send — what happened?" | Common causes: you imported a new list with outdated or unverified addresses, you sent to a Subscription you haven't mailed in a long time (addresses went stale), or there's a technical issue like a DMARC policy change on your domain. Check the bounce codes — if they're mostly hard bounces (2xxx), it's a list quality issue. If they're mostly technical bounces (4007–4009), check your authentication setup. If the spike is isolated to one send and doesn't repeat, it may have been a temporary issue on the receiving side. |
"A Profile was blocked after 3 hard bounces — can I unblock them?" | Apsis One automatically stops sending to Profiles with 3 hard bounces to protect your sender reputation. The Profile's consent is not removed — they're just excluded from sends.
If you believe the address is now valid again (e.g. the recipient fixed a mailbox issue), you need to delete the profile and import it again. Resetting bounces is not possible. |
"My spam complaint count is 0 but emails are landing in spam — why?" | The spam complaint count in your report only shows complaints sent back to Apsis via Feedback Loops (FBLs). Not all providers participate — Gmail, for example, does not send complaints through FBLs. Your emails may be landing in spam due to content triggers, missing DKIM/DMARC, poor sender reputation, or low engagement rates — none of which generate a visible complaint in your report. Set up Google Postmaster Tools for Gmail visibility, and review the Keep Deliverability High article for a full checklist. |
"I see bounce code 9999 — what does that mean?" | Code 9999 (Soft – Unknown) is a catch-all code used when the receiving server's rejection reason doesn't fit a standard category. Common causes include greylisting, rate limiting, server timeouts, or vague content-level filtering. Since it's a soft bounce, Apsis One retries delivery automatically. If you see a large number of 9999 bounces in a single send, it may indicate throttling or temporary issues on the receiving end — usually resolves on its own. |
What's next?
Keep Deliverability High — Consent management, content guidelines, warm-up process, and the email journey to the inbox.
Email Authentication – Safe Sending — SPF, DKIM, DMARC, IP management, and TLS.
Email Report — Full guide to reading and acting on your email performance data.
Data tags and Segments — Create Segments to exclude bounced or inactive Profiles from future sends.