My Bounce Rate Is Too High

Bounce rate is the strongest reputation signal you control. Every receiver — Gmail, Outlook, Yahoo, the corporate mailservers — watches it. Past 2%, you're being noticed. Past 5%, you're on a watchlist. Past 10%, you're getting blocked. This guide explains what's actually being measured, what counts as a bounce, the categories of bounces, and how to bring the number back down.

What "bounce rate" measures

It's the percentage of your sent messages that the recipient server refused to accept and delivered back to us with a non-delivery report.

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

We compute it per domain (not per mailbox), over rolling windows (24 hours, 7 days, 30 days). Find your bounce rate on the Domains page → click a domain → Email stats tab.

Healthy ranges

The 10% threshold isn't arbitrary — that's roughly the level at which Gmail and Microsoft start refusing your mail outright.

Hard bounces vs soft bounces

Receivers report two categories:

Hard bounces

"This address doesn't exist." Permanent. The recipient server tells us "no such mailbox" and we know not to try again.

• 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 — Permanent block. The recipient refuses your domain entirely.

Hard bounces hurt the most. They tell receivers you're sending to addresses you shouldn't even know about — characteristic spammer behaviour.

Soft bounces

"This address exists but can't take mail right now." Temporary. The receiver may accept it later.

• 4.2.2 — Mailbox over quota. The recipient inbox is full.
• 4.5.1 — Greylisted. First time we've seen this sender; the receiver wants us to try again later.
• 4.7.0 — Temporarily blocked. Rate-limiting or temporary reputation issue.

We retry soft bounces a few times on a backoff schedule. If they keep failing for several days, they're escalated to hard-bounce status.

Hard bounces count fully against your bounce rate. Soft bounces count proportionally — multiple failed retries that eventually time out count like one hard bounce.

Common causes of high bounce rate

Bought, scraped, or old lists

The single biggest cause. Bought lists 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: don't send to bought lists. There's no salvaging this without complete list rebuild.

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. The verifier categorises each address as Safe / Valid / Risky / Invalid / Unknown. Drop Invalid; consider dropping Risky depending on tolerance.

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

Receivers (especially Microsoft) plant fake addresses across the internet. Anyone sending to those addresses is flagged as "harvested email" — list-buyer behaviour. One spam trap hit can hurt for weeks.

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 built-in bounce protection

A few mechanisms reduce bounces automatically:

MX pre-validation

Before queuing your message for delivery, we check whether the recipient's domain has valid MX (or fallback A) records. Domains without DNS records can't receive mail. We silently filter those messages out — they never even leave our server. You don't see them as bounces because they never reach the bounce stage.

Result: typos like alice@gnail.com (no MX) bounce in 0 seconds at our edge. They don't count against your reputation. They show up in your stats as "filtered" rather than "bounced".

Recipient suppression

After a hard bounce, the recipient address is automatically added to a per-domain suppression list. Future sends to that address are silently dropped before they go out — preventing repeated bounces to a known-bad address.

If a user mistakenly hard-bounced (e.g. their mailbox was temporarily disabled), you can remove them from suppression via Domains page → Suppression list → Remove. Use sparingly; suppression is the right default.

Domain alerts

If a domain's bounce rate exceeds 10% in a 24-hour window (and you've sent at least 20 messages — to avoid noise on low-volume domains), you get an email alert. This is your warning to pause and clean up before reputation damage compounds.

How to fix a high bounce rate

Step 1 — Stop sending

If you're over 5%, the most important step is to pause for 24 hours. Continuing to send while bouncing makes everything worse.

Step 2 — Identify the bad addresses

• Export your current list.
• Run it through the Email Verifier. For each address you'll see one of:
  • Safe — confidently deliverable.
  • Valid — probably deliverable.
  • Risky — catch-alls, role accounts, recently-active domains with high risk profile.
  • Invalid — confirmed bad. Remove immediately.
  • Unknown — couldn't verify, treat as risky.
• Update your list to keep only Safe + Valid. Optionally include Risky if your tolerance is higher.

Step 3 — Warm up again

After cleaning the list, don't go back to full volume immediately. Start at 10% of your previous volume and ramp up gradually over a week. This rebuilds reputation that the bounce-storm damaged.

Step 4 — Audit how new addresses join

• Are you collecting via single opt-in? Switch to double opt-in (send a confirmation email; only enrol addresses that click through).
• 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

After cleanup, watch the Email stats panel daily for a week. You want bounce rate trending down. If it stays elevated, something in your list is still bad.

Forwarding-related bounces

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

• The forward-to address's domain is validated on save (we check MX). If invalid, save fails immediately.
• If forwarding is set but the forward-to address bounces (mailbox over quota, disabled, etc.), the bounce counts against your domain's reputation — even though you didn't send to it directly.
• Periodically verify forward-to addresses are still valid. People forget their forwards point at a personal email that's no longer in use.

Soft-bounce-specific issues

If your bounces are mostly soft (not hard):

• Greylisting — first contact with a new receiver triggers greylisting at some servers. We retry on a back-off; soft bounces should clear within hours.
• Recipient mailbox full — you can't fix this from your side. The recipient needs to clear space. Stop sending to that address until they confirm space.
• Temporary network issues — receiver-side outages cause batches of 4xx errors. Usually clears within hours.

If a soft-bounce category persists for days against the same domain, it's effectively a hard bounce and counts that way.

Common questions

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

For sustained over-10% periods, yes — your account may be placed in deliverability suspension. The dashboard shows: "We've temporarily paused outbound mail because too many of your recent messages were rejected by recipient servers." Contact support to discuss the list hygiene path before lifting.

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

Yes. If you send to alice@yourdomain.com and Alice's mailbox was deleted, that's a hard bounce and counts.

Does TrekMail count bounces from forwarding?

Yes. If your mailbox forwards to a Gmail that's been deleted, the bounce counts.

Can I see which addresses bounced?

Yes — Domains page → your domain → Suppression list shows all suppressed (hard-bounced) addresses with the reason and timestamp.

Can I bulk-remove the suppression list?

Not via UI. If you have a clean replacement list and want to clear everything, contact support. Generally you want suppression to stay — it's protecting your reputation.