How do bounces interact with feedback loops?

Bounces and feedback loops both tell you something went wrong, but they're measuring completely different problems. A bounce says the email couldn't be delivered at all. A feedback loop (FBL) complaint says the email arrived just fine, but the recipient was so unhappy they hit "mark as spam." Two different failure modes. Both damage your sender reputation if you ignore them.

Here's where it gets interesting: they interact through your suppression list. When a hard bounce comes back, that address is invalid and goes straight to suppression. When an FBL complaint arrives (usually via Gmail's postmaster tools or Yahoo Mail's complaint feedback), that person should also be suppressed immediately, even though their address technically works. They've told you, in the loudest way available to them, that they don't want your emails.

The problem most senders run into is that these two signals live in separate places. Bounces come back through your ESP. FBL complaints arrive through a separate feedback loop registration you have to set up with mailbox providers directly. If your suppression system isn't pulling from both, you've got gaps.

From a reputation standpoint, FBL complaints are often the more urgent signal. A spike in complaints can trigger throttling or blocking much faster than a gradual rise in bounce rate. Hard bounces matter too (especially if your bounce rate climbs above 2%), but a complaint rate above 0.1% at Gmail will start affecting your inbox placement almost immediately.

A well-run setup treats both as inputs to the same suppression system. Regardless of how you learned about the problem (the address failed, or the person complained), the result is the same: that address gets suppressed and doesn't get mailed again. No separate "bounced" list and "complained" list sitting in different spreadsheets. One source of truth.

Tracking them together also reveals patterns worth knowing. If a campaign generates both high bounces and high complaints, that's a strong signal the list segment wasn't clean or consented. Bounces alone might just mean old data. Complaints alone might mean a message that missed the mark. Both together usually points to a list health problem worth investigating at the source.

If you want to check whether your current setup is handling both signals correctly, our SOS hotline is free and we're happy to walk through it with you.