Understanding bounces & Letterhead's bounce handling

When an email is returned to the sender, it’s called a bounce. Bounces come in two types, and understanding the difference helps you troubleshoot delivery issues and keep your list healthy.

Soft bounces

A soft bounce is temporary — the recipient’s mail server received the email but couldn’t deliver it to the inbox. Common reasons:

1. The recipient’s mailbox is full.
2. The message is too large for the recipient’s mailbox.
3. The recipient’s email server is down or having issues.
4. The email was blocked by the recipient’s spam filter.

Soft bounces usually resolve themselves; providers retry a few times before treating the address as a hard bounce.

Hard bounces

A hard bounce is permanent — the email couldn’t be delivered because the address is invalid, non-existent, or blocked. Common reasons:

1. The address is invalid or doesn’t exist.
2. The domain has been closed or no longer exists.
3. The address is a known spam trap.
4. The recipient’s server has blocked the sender’s domain.

Hard bounces hurt deliverability — too many can get your domain flagged as a spammer — which is why cleaning invalid addresses off your list matters.

How Letterhead handles bounces

• Hard bounce: the address immediately moves to the Bounced (Cleaned) status. It receives no further emails and isn’t billed on your account.
• Soft bounce: Letterhead keeps sending to the address until it soft-bounces several times in a row, at which point it’s treated as a hard bounce and moved to the bounced status. The exact threshold varies by circumstance.

You can see bounces in each newsletter’s metrics report, and each contact’s profile shows their bounce history — hard/soft counts plus mail-server reasons — along with which newsletters they’re suppressed from and why. These profile views may need to be enabled for your account — contact support.

Resubscribing a bounced address

We don’t recommend it — it’s best for the reader to subscribe with a different address. Letterhead suppresses Cleaned emails to prevent further delivery issues and protect your sender reputation. If you’re confident the address is now valid, you can edit the subscriber and change their status to Pending confirmation, save, then edit again to Subscribed.

For more on list health, see List Optimization and Working in Audience.