Email Bounces Explained: Hard, Soft and When to Stop Sending to an Address

What is an email bounce?

A bounce is a refusal. Your sending service hands the message to the recipient's mail server, and the server answers with a reply code. RFC 5321 splits the failures in two. A 4yz reply is a transient failure: the action did not happen, but "the error condition is temporary, and the action may be requested again." A 5yz reply is a permanent failure: the sender "SHOULD NOT repeat the exact request." RFC 3463 gives the same split in its enhanced status codes, where a 4.X.X code is a persistent transient failure and a 5.X.X code is a permanent one that is "not likely to be resolved by resending the message in the current form."

What is the difference between a hard and a soft bounce?

Hard means permanent and soft means transient. Resend, the service MAJ Leads sends newsletters through, uses three labels on its bounce page:

Resend adds one useful note: a transient result may come from an autoresponder, which is not a permanent problem. A full mailbox on a staff address is a common cause in a business list. A wrongly typed address, such as a misspelt domain, is the usual cause of a hard bounce.

When should you stop sending to an address?

After a hard bounce, straight away. RFC 5321 says the sender should not repeat the same request, and nothing is gained by trying again. After a soft bounce, retry, but not forever. Google's sender guidelines say to reduce the sending volume if messages start bouncing or being deferred, and to "automatically unsubscribe recipients who have multiple bounced messages." Google does not say how many is multiple.

Complaints are the other number to protect. The same guidelines say to keep the spam rate reported in Postmaster Tools below 0.10% and to avoid ever reaching 0.30% or higher. Bounces and complaints are separate numbers, and you need to watch both. Our guide to the bulk sender rules covers the rest of what Gmail, Yahoo and Microsoft ask for.

What does MAJ Leads do with a bounce?

Three things about those rules. First, the three-in-30-days limit is our own choice. No standard or provider sets it, and a different team could pick a stricter number. Second, a suppression applies to the address, not to one lead record, so every lead that shares it is covered. Third, suppressed addresses are checked again when a campaign is about to send, not only when it was planned, and a suppressed address is skipped when someone tries to add it to a list.

What should you do about a bounced address?

1. Look at the address. A typo such as a missing letter in the domain is worth fixing by hand, once.
2. Ask the person for another address by the channel you do have, such as a call or a WhatsApp message from your rep.
3. Do not add the address back to a list to see whether it works. The suppression is there to stop that.
4. If many addresses from one source bounce, look at the source. A list that was typed in a hurry or that is old will bounce more than one collected on your own form. Our guide to buying an email list explains why that route is risky.

Sending from a domain that is set up properly helps too, because some refusals are about the sender, not the address. Our SPF, DKIM and DMARC guide shows how to do that.

Where does this leave your newsletters?

Newsletters in MAJ Leads go to your own leads and customers. The bounce rules above run without anyone watching a dashboard, and the campaign report shows bounced, complained and unsubscribed counts. Read why open rates are only a rough signal next. See how it works and pricing.