Diagnostics

Fix email spam issues

Start from the bounce you actually received. Each page below is one real SMTP response — what the server means by it, why it happens, and the order to fix it in.

Find your error

• 550 5.7.1 — Our system has detected that this message is likely unsolicited mail · Gmail, Google Workspace
• 554 5.7.1 — Message rejected due to content restrictions · Outlook, Microsoft 365, Corporate filters, SMTP

Read the code before you change anything

The first digit decides whether you have a problem at all. A 4.x.x is temporary — the sending server retries by itself and you usually need do nothing. A 5.x.x is permanent: that message is refused and resending it changes nothing.

The second and third decide whose problem it is. A 5.1.1 is the recipient — the address does not exist. A 5.7.x is you — a policy refusal about your reputation, your authentication, or your content, in roughly that order of weight. Most guides treat every bounce as a content problem, which is why the advice so often fails to work.

The order that actually fixes it

1. Check SPF, DKIM and DMARC — free, instant, and the most common single cause.
2. Check the domain against blocklists — one listing can refuse every message.
3. Look at sending history. A cold domain, or one that ramped volume quickly, gets filtered no matter how good the copy is.
4. Score the content — worth doing before every campaign, but last in the order.

Frequently asked questions

How do I fix emails going to spam?

Work in this order, because it is the order the receiving server weighs things. First confirm SPF, DKIM and DMARC pass for the exact sending domain. Second, check the domain and IP against the major blocklists. Third, look at sending history - a cold or newly-ramped domain gets filtered regardless of how clean the copy is. Only then rewrite the content. Most people start at the content and wonder why nothing changes.

Why did my email bounce with a 5.7.1 error?

A 5.7.x is a policy refusal about you, the sender - not a statement that the recipient address is wrong. The server accepted the connection, looked at the message and the reputation behind it, and refused. That is different from a 5.1.1, which means the address does not exist.

Is a bounce permanent or will it retry?

A 5.x.x code is permanent - the message will not be retried and resending the same mail hits the same wall. A 4.x.x is temporary, usually rate limiting, and the sending server will retry on its own. Check the first digit before you do anything else.

Can I fix this by rewriting the subject line?

Rarely on its own. Content is one input among several, and it is the one with the least weight when the sending domain has no reputation. Rewriting helps once authentication passes and the domain has sending history - before that it is the last thing to change, not the first.