Why Is My Bounce Rate So High?

Bounce rate is an important delivery signal. A high rate usually means the recipient list needs attention, and it can make future mail less likely to be accepted. This guide explains what TrekMail measures, how to read the recent-bounce details, and how to make the next send safer.

What "bounce rate" measures

It is the share of outbound delivery attempts that ended in a hard or soft bounce.

bounce rate = (bounced messages) / (total sent) × 100%

TrekMail shows delivery statistics per domain for the most recent 30 days. Open Domains, choose the domain, then open Email stats. The same page includes a recent-bounces table with the recipient, date, SMTP code, and response.

Healthy ranges

Separately, TrekMail's bounce-rate safeguard can pause sending when a domain reaches 10% or more in a 24-hour period with at least 20 attempted messages. This is a safety control, not a prediction of how any individual recipient provider will react.

Hard bounces vs soft bounces

Receivers report two categories:

Hard bounces

These usually mean the recipient address cannot receive mail. The SMTP response is the best source for the exact reason.

• 5.1.1: User not found. The mailbox doesn't exist.
• 5.1.2: Domain not found. The domain doesn't exist or has no MX.
• 5.7.1: A policy or permission refusal. It is not always a permanent missing-mailbox error.

Repeated hard bounces are a strong sign that the list contains invalid or outdated recipients.

Soft bounces

These usually describe a temporary delivery problem. Keep the recipient's exact SMTP response, because it tells you whether the problem is capacity, a temporary policy, or a network issue.

• 4.2.2: Mailbox over quota. The recipient inbox is full.
• 4.5.1: The receiver is temporarily deferring mail.
• 4.7.0: Temporarily blocked. Rate-limiting or temporary reputation issue.

Both hard and soft bounces appear in the domain's delivery statistics. Do not assume a temporary response will resolve on its own; reduce repeat sends to the same address until you understand the response.

Common causes of high bounce rate

Bought, scraped, or old lists

Bought lists often contain:

• Addresses that never existed.
• Addresses that existed years ago but the employee left.
• Spam-trap addresses planted specifically to catch list-buyers.
• Addresses for receivers that hard-fail on contact (security teams' role accounts).

Solution: do not send to bought lists. Rebuild the list through a clear opt-in process.

Old lists you haven't cleaned

A list that was fine 2 years ago has degraded. People change jobs, mailboxes get deleted, domains expire. Sending to a 2-year-old list cold hits all of those at once.

Solution: run the list through TrekMail's Email Verifier before sending. Remove invalid addresses and make a deliberate decision about risky or unknown results.

Typos in legitimate addresses

Someone signed up as alice@gnail.com (instead of gmail.com). The signup form didn't validate. Now you send and bounce.

Solution: enforce typo detection on signup forms (most form-builders have a gmail/yahoo typo plugin). And periodically verify your active list.

Spam traps

Spam traps are addresses used to identify unwanted mail. Sending to them can damage delivery performance, especially when the address came from a purchased or scraped list.

Solution: only send to addresses you obtained through clear opt-in. If you can't trace where an address came from, don't email it.

Domain warmup violations

Sending high volume from a brand-new domain triggers receiver scepticism. Many addresses temporarily reject; you see bounces that shouldn't have been bounces.

Solution: follow the warmup curve (40% of plan limit days 1-3, 70% days 4-7, 100% day 8+). See Domain Warmup Rules.

TrekMail's bounce safeguards

These safeguards help prevent repeated problems, but they do not replace list cleanup:

Check the list before you send

Do not rely on the sending system to remove invalid addresses before a campaign. Use TrekMail's Email Verifier for an imported or old list, then remove addresses reported as invalid and treat risky or unknown results carefully.

Recipient suppression

TrekMail can suppress a recipient after an outbound hard bounce so the same bad address is not repeatedly sent to from the same account.

How fast an address gets suppressed depends on why it bounced:

• Clearly permanent recipient failures such as "user unknown" or "no such mailbox" can be suppressed after the first hard bounce.
• Ambiguous or recoverable 5xx responses such as a full mailbox, quota, or policy response use a three-bounce threshold.

Hard-bounce suppressions normally expire after 14 days and reset their bounce count. Complaint and manual suppressions do not automatically expire.

If an address was suppressed in error, contact support with the domain, recipient address, and bounce response. Do not repeatedly remove or resend to an address without correcting the underlying cause.

Domain alerts

The bounce-rate safeguard uses a 10% threshold over 24 hours and waits until there are at least 20 attempted messages. Use the recent-bounces table to find the cause before restarting the campaign.

How to fix a high bounce rate

Step 1: Pause the affected campaign

If the domain is at 5% or above, stop the campaign that produced the bounces. Do not keep retrying the same batch while you investigate.

Step 2: Identify the failing recipients

• Export your current list.
• Run it through the Email Verifier. For each address you'll see one of:
  • Safe and Valid results are the lowest-risk choices for a new campaign.
  • Risky and Unknown results need a deliberate decision based on your relationship with the recipient.
  • Invalid results should be removed.
• Compare verifier results with the exact bounce response in the Email stats table before changing records.

Step 3: Resume gradually

After cleaning the list, restart with a small group of recipients who expect the message. Increase volume only while the bounce rate remains healthy. The correct pace depends on the domain's history and the type of mail; a fixed percentage cannot guarantee delivery.

Step 4: Audit how new addresses join the list

• Are you collecting via single opt-in? Consider double opt-in, where a recipient confirms the subscription before being added.
• Are you buying or renting lists? Stop.
• Are you scraping addresses from LinkedIn / databases? Stop.
• Are your signup forms validating email format? Add typo detection.

Step 5: Monitor the next sends

Watch Email stats and the recent-bounces table after each small batch. If the rate stays high, stop and investigate the new responses before increasing volume.

Bounces related to forwarding

Each mailbox can forward to an external address. If you've set up forwarding:

• A forwarding destination can become unavailable after the rule is created.
• TrekMail keeps forwarding-related bounces separate from the domain's outbound bounce-rate calculation.
• Review forwarding destinations periodically, especially when they point to a former employee's or personal mailbox.

Soft-bounce-specific issues

If your bounces are mostly soft (not hard):

• Temporary deferral: keep the SMTP response and avoid repeated sends until the receiver accepts mail again.
• Recipient mailbox full: the recipient needs to make space. Do not keep sending to that address in the meantime.
• Temporary network issue: a receiver-side outage can affect many addresses at once. Check whether the same response appears across the batch.

If the same temporary response persists, treat the address or recipient provider as high risk and investigate before sending again.

Common questions

Will TrekMail block my sending if I'm over 10%?

The bounce-rate safeguard can pause sending at 10% or more over 24 hours, after at least 20 attempted messages. If this happens, stop the affected campaign, review the recent-bounces table, clean the list, and contact support with the domain and bounce responses if you need help.

Does TrekMail count internal-to-internal bounces (one TrekMail mailbox to another)?

The Email stats calculation is based on outbound delivery events for the domain. The recent-bounces table shows the recipient and SMTP response so you can investigate the specific case.

Does TrekMail count bounces from forwarding?

Forwarding-related bounces are tracked separately and excluded from the domain's outbound bounce-rate calculation.

Can I see which addresses bounced?

Yes. Open the domain's Email stats tab and expand the recent-bounces table. It lists hard and soft bounces from the last 30 days, including the recipient, date, SMTP code, and response.

Can I bulk-remove the suppression list?

Do not clear suppressions as a way to force delivery. Correct the recipient list first. If you believe a particular address was suppressed in error, provide its address and bounce response to support for review.