When Gmail says "Message not delivered," the heading on the notice is the first clue and the technical details underneath are the second. Address not found is yours to fix. Domain not found is usually a typo. A misconfigured remote server is the recipient's problem, and nothing you change will help. Read the heading, then find the one line that says what the other server returned.
Gmail sends these as a "Delivery Status Notification" from Mail Delivery Subsystem. Below, the common headings one at a time: what each means, who can fix it, and the 30-second check that tells you which kind you have.
The headings, who can fix each, and what to do
| Heading in the notice | What it means | Who can fix it |
|---|---|---|
| Address not found | No mailbox at that address, or it can't receive mail | You: check the spelling, then find another address |
| Domain not found | The part after the @ doesn't exist in DNS | You, if it's a typo. Nobody, if the domain has lapsed |
| Message blocked | Their server refused it on policy grounds | Depends on the code. See the blocked-message guide |
| Message not delivered ... remote server is misconfigured | Their mail setup is broken or points nowhere | Only the recipient |
| "rejected by the server for the recipient domain" | Their gateway said no, with its own code | Read the code on the next line |
| Delivery incomplete, or message delayed | A temporary problem; Gmail keeps trying | Nobody yet. Wait |
Google's help page for bounced mail lists the same families of cause: a bad address, a message flagged as spam, the sender's daily limit, a temporary problem at the recipient's end, and a full inbox. The table above sorts them by what you can do about them.
Address not found
This is the usual one. Check for the three typos that account for most of them: a missing letter in the domain, a trailing period or space, and the wrong ending (.com for .net). If the spelling is right, the person has left or the address never existed. Do not retry. Remove it, and find a current one. How to find a business owner's email address covers where to look.
Domain not found, and the misconfigured server
These two look alike and feel hopeless, but the check is quick. Wren sells wholesale linens to boutique hotels. In a batch of 30 emails she got four notices. One said Address not found, a typo ("hotell"). One said Domain not found. One said the remote server was misconfigured. One said Google's message had been "rejected by the server for the recipient domain."
For the second and third she ran the same test. Go to a free MX lookup tool (or on Windows, open a command prompt and type nslookup -type=mx and the domain). It lists the servers that receive mail for the domain. For the hotel with Domain not found, the lookup returned nothing at all: the domain had expired when the property was renamed. For the one with a misconfigured server, the lookup showed no mail servers, which usually means the domain has a website but never set up email, or the setup was removed. In both cases the hotel doesn't receive mail at that address, and no change on Wren's side could help.
What she did next was the useful part. She called the front desk, asked for the manager's current email, and was given one at a different domain, a Gmail address. A bounce like this is a sign the contact record is out of date, and a phone call or the property's contact form often gets you the live address in a minute.
Blocked, or rejected by their server
The fourth notice said "Google tried to deliver your message, but it was rejected by the server for the recipient domain," followed by a line starting "The error that the other server returned was" and a code. That code decides everything. 5.1.1 is a bad address. 5.7.x is a policy refusal. If a code in that family appears on many companies at once, the problem is on your side: see your message has been blocked in Gmail and what the error codes mean. If it is only at one company's domain, it's their gateway, and you need another way in. Wren's fourth was a hotel group whose mail system rejects mail from addresses it hasn't seen before.
What you can fix and what you cannot
A short sort. You can fix a typo, an outdated contact, an authentication failure on your own domain, a volume spike, a link pattern, an oversized attachment. You cannot fix a recipient's expired domain, a missing mail server, their gateway policy, or their full inbox. Spending an hour trying to fix the second group is the most common waste of time with bounces. What works is to change the route: a call, the contact form on their site, a different address at a different domain, or a note through someone who knows them.
A delayed message is not a failed one
The "Delivery incomplete" or "Message delayed" notice scares people into resending. Don't. Gmail keeps retrying for a long stretch, around two days, and tells you if delivery fails for good. The usual causes are a recipient server that is down or busy, or one that is slow to accept mail from unfamiliar senders. If you send the same email again, the recipient may get two copies the moment their server recovers, which looks careless on a cold email. Wait for the final notice, and only then decide.
Cleaning the address before you resend
Write what happened beside the address in your sheet before you touch anything: the heading, the code, the date. Delete the dead ones. Correct the typos and resend those once. Send nothing to the "delayed" ones until the final notice arrives, because Gmail is still trying and a second copy only duplicates. For the habit that prevents most of this, verify addresses before you send. If bounces on a batch are above a few in a hundred, the bounce-rate guide has the pause rule, and SPF, DKIM and DMARC is the next place to look when blocks start appearing.
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