Email that worked yesterday is bouncing today. The bounce message names the cause, and it is almost always a changed DNS record, a broken SPF record, or a blocklist. Here is how to diagnose and fix each.

Nothing changed on your end, or so it feels, and suddenly messages that always landed are bouncing back or vanishing into spam. Sudden undeliverability is unsettling because email is invisible until it breaks, but it rarely breaks at random. Something shifted in your DNS, your authentication, or your sending reputation, and the receiving servers reacted. The reassuring part is that the bounce itself usually tells you which one, so you are diagnosing, not guessing.

The Short Version: read the bounce message first, because the code and text name the cause. From there, three problems account for most sudden failures. A DNS record that was edited, deleted, or expired during a host or registrar change can break your MX or authentication overnight. An SPF record that now fails, from a duplicate record, too many lookups, or a new sending service you never added, will get mail rejected. And your domain or IP landing on a blocklist like Spamhaus causes instant rejections. Diagnose in that order, fix the root cause, and only then request any delisting.

So why did your email suddenly stop delivering?

Because a receiving server decided to reject or hide your message, and it left a reason in the bounce. Before touching any settings, open the bounce notification and read the status code and text, since that single line points you to the right fix. A code around 550 5.7.1 often signals a policy or blocklist rejection, a message about SPF or DKIM points at authentication, and a host-not-found error points at DNS or MX. Once you know the category, work through the three usual causes below in order, DNS, then SPF, then blocklists, rather than changing everything and hoping. Fixing the wrong thing wastes a day while your mail keeps bouncing.

A DNS record changed or disappeared

The most common trigger for sudden failure is a DNS change you may not have made yourself. Migrating hosts, switching registrars, or editing your zone can drop or overwrite the records email depends on, your MX for routing and your SPF, DKIM, and DMARC records for authentication. If the MX vanished, mail has nowhere to go; if an authentication record broke, receivers may reject or spam your messages. Changes also take time to propagate, so a recent edit can cause intermittent failures for hours. Pull up your live DNS with a lookup tool and confirm the MX and authentication records are present and correct, especially if anything about your hosting or domain changed just before the trouble started. Our guide to the questions to ask before switching a business email domain covers the records that most often get lost in a move.

Your SPF record broke

SPF is a frequent and sneaky cause, because it can break without you editing it directly. Three failures dominate. First, a domain may publish only one SPF record, so adding a second creates a permanent error and mail fails. Second, SPF allows a maximum of ten DNS lookups, and chaining too many services pushes you over that limit into a permerror that receivers treat as a fail. Third, adopting a new sending service, a CRM, a newsletter tool, a help desk, without adding its include to your SPF means every message it sends fails authentication. Consolidate to a single SPF record, trim or flatten the lookups to stay under ten, and add the include for every service that sends on your behalf, then confirm your closing mechanism is set correctly. Google’s reference on defining an SPF record spells out the syntax.

Your domain or IP is on a blocklist

If authentication and DNS check out but mail is still rejected, your sending reputation is the likely problem. Blocklists such as Spamhaus are databases of IPs and domains flagged for spam, and receiving servers check them during the connection, rejecting anything listed. A sudden listing usually follows a spam complaint spike, a compromised account sending junk, aggressive cold outreach, or a bad neighbor on a shared IP. Check whether you are listed with a tool like MXToolbox’s blacklist lookup, and if you are, resist the urge to request removal immediately. Fix the root cause first, secure any compromised account, stop the sending pattern that triggered it, and tighten authentication, because Spamhaus and others will simply relist you otherwise. Spamhaus explains the process in its guidance on handling bounced email. Once the cause is resolved, request delisting, and blocks often clear within 24 to 72 hours.

Bounce or symptom	Likely cause	Fix
Host not found or no route	MX record dropped or misedited	Restore the correct MX; allow propagation
SPF or DKIM failure in the bounce	Broken or missing authentication record	Repair the record; add missing includes
SPF permerror	Duplicate record or over ten lookups	Use one record; trim lookups under ten
550 5.7.1 policy rejection	Domain or IP on a blocklist	Fix the cause, then request delisting
Intermittent failures after a change	DNS still propagating	Confirm records; wait out the TTL

When email breaks overnight, the bounce message names the category, so start there and work through DNS, SPF, and blocklists in order rather than changing settings blindly. Frequently Asked QuestionsWhy did my email suddenly become undeliverable when nothing changed?

Something almost always changed, even if not by your hand. A host or registrar migration can silently drop DNS records, a new sending tool can break SPF, or a spam complaint can trigger a blocklist listing. The bounce message is the fastest clue, since its status code and text name the category. Read that first, then check your live DNS, your SPF record, and the major blocklists in turn to find which one shifted.

What does a 550 5.7.1 bounce mean?

It is a policy rejection, meaning the receiving server refused your message rather than failing to route it. A common reason is that your sending IP or domain appears on a blocklist, though strict authentication or content policies can also produce it. Read the full bounce text for specifics, check whether you are listed on Spamhaus or similar, and confirm your SPF, DKIM, and DMARC pass. Resolve the underlying reason before asking for any removal.

How do I know if my SPF record is the problem?

Look for SPF wording in the bounce, then inspect your published record. Two red flags are common: more than one SPF record on the domain, which causes a permanent error, and more than ten DNS lookups in the chain, which triggers a permerror that receivers treat as a fail. Also confirm every service that sends for you, your CRM, newsletter tool, and help desk, is included. Consolidate to one record, reduce the lookups, and add any missing includes.

How long does it take to get off an email blocklist?

Once you have fixed the root cause, many blocks clear within 24 to 72 hours, and some auto-expire after the triggering activity stops. Requesting delisting before you have resolved the cause is counterproductive, because the blocklist will relist you when the bad behavior continues. Secure compromised accounts, stop the sending pattern that flagged you, and confirm clean authentication first, then submit the removal request and monitor delivery over the following days.

Should I fix DNS or reputation first?

Fix DNS and authentication first, because they are within your direct control and often the actual cause, and because a clean DNS setup is a prerequisite for getting off a blocklist anyway. Confirm your MX routes mail and your SPF, DKIM, and DMARC pass, then turn to reputation and blocklists. Working in that order avoids the common trap of chasing a delisting while a broken SPF record keeps your mail failing regardless.

Key Takeaways

• Read the bounce message first; its status code and text name the cause and save you hours of guessing.
• A dropped or edited DNS record, often from a host or registrar move, breaks routing or authentication overnight.
• SPF fails from a duplicate record, more than ten lookups, or a new sending service missing from your includes.
• A 550 5.7.1 rejection usually means your domain or IP is on a blocklist like Spamhaus.
• Fix the root cause before requesting delisting, or you will simply be relisted.

What To Do Next

Sudden undeliverability feels like a black box, but it is a short checklist once you let the bounce lead. Open the failure notice and read the code, then confirm your DNS in a lookup tool, since a missing MX or a broken authentication record from a recent move explains a large share of these. If DNS is clean, inspect your SPF for a duplicate record, too many lookups, or a service you forgot to include. Only when routing and authentication pass should you check the blocklists, fix whatever put you there, and then ask for removal. Work top down, change one thing at a time, and re-test after each, so you know which fix restored delivery. For a related case where messages pass authentication yet still bounce, see our DMARC-passes-but-bounces troubleshooting flow, and browse Venture-Lab’s Growth Hacking section for more.