📉 Hard And Soft Bounces

A bounce is an email that could not be delivered. Not every bounce means the same thing, so the Mailer does not treat them the same. A dead address is blocked at once. A temporary hiccup is only noted, because real people with a full mailbox should stay on your list.

A hard bounce:

The address or the whole domain does not exist. Trying again cannot help, so the address is added to your suppression list straight away, as Bounced, with the reason the receiving server gave. It is never emailed again unless you set it free with Allow again.

A soft bounce:

Something temporary went wrong: the mailbox was full, the server was busy, or the message was greylisted. These usually fix themselves, so a soft bounce does not block the address. It is recorded, and the next email is sent as normal.

When a soft bounce becomes a block:

If an address soft bounces 5 times within 90 days, it is treated as gone and added to your suppression list as Bounced. The reason reads, for example, Soft-bounced 5 times in the last 90 days; treated as gone, followed by the last reason the server gave. Only soft bounces inside those 90 days count, so an address that had one bad week last year does not start part way to being blocked.

How the Mailer tells them apart:

1. If your sending service says whether the bounce was hard or soft, the Mailer uses that.
2. Otherwise it reads the receiving server's reason. Permanent codes and messages such as user unknown or does not exist count as hard.
3. Anything it cannot be sure about counts as soft. Being careful keeps real people on your list.

Every bounce, hard or soft, is logged with its reason and the sending service that reported it, so you always have the full history. A bounce can also start an automation, for example to tag the person or let you know.

Getting bounces reported to you:

Bounces reach the Mailer through your sending service's webhook.

1. Go to Delivery, then Sending.
2. Under Bounce and complaint webhook, find your sending service and click Copy URL.
3. In your sending service's dashboard, add a webhook pointing at that address.
4. Turn on the bounce, spam complaint and unsubscribe events.

The webhook card appears for services with an API, such as Amazon SES, SendGrid, Mailgun, Postmark, Brevo, SparkPost, SMTP2GO, Resend, Mailjet and Elastic Email. The address ends in a secret that stops anyone else sending you fake events, so keep it private.

Seeing your bounces:

• Delivery, then Deliverability: pick Bounced in the type filter and click Search to list every blocked address, with the reason and the service that reported it.
• Reports: the List health panel counts bounces in any date range.
• The Get Started page repeats the rule in its Worth knowing card.

A real example:

Leafwise Gardening sends through Amazon SES. One evening a reader's mailbox is full, SES reports a soft bounce, and the Mailer simply notes it; the next newsletter reaches her as usual. The same week, an old address from Anna's import no longer exists. SES reports a hard bounce, and the address appears on the suppression list as Bounced with the reason Hard bounce, so it is never mailed again.

Tips:

• Set up the webhook on day one. Without it, the Mailer cannot know about bounces.
• Keep bounces under 2% of what you send. A higher rate usually means an old list. See List Health: Unsubscribes, Bounces And Complaints.
• Clean a list you have not mailed for a long time before you send to it. See The Audience Health Check.