In this guide · 8 sections
Short answer
First ask a sender for their bounce message, then check that your domain hasn't expired and your MX records still point to Microsoft 365 or Google. If they do, run a message trace (Microsoft) or Email Log Search (Google), then check storage, inbox rules, forwarding and quarantine.
First: is it everyone, one person or one sender?
The pattern of what's missing tells you where to look. Spend two minutes on this before changing anything.
| What you see | Most likely cause | Where to look |
|---|---|---|
| Nobody in the company gets external email | MX records changed, domain expired, DNS moved | Registrar and DNS records |
| One person gets nothing | Mailbox full, inbox rule, forwarding, licence removed | That user's mailbox and settings |
| Mail from one sender or company missing | Junk, quarantine, blocked sender, their own problem | Junk folder, quarantine, block lists, message trace |
| Mail stopped right after a website change | New host or builder replaced your DNS | MX records at the current DNS host |
| Senders get a bounce message | The bounce code names the reason | Ask them to forward the full bounce |
A bounce message (also called a non-delivery report or NDR) is the single most useful clue. Microsoft's guide to Exchange Online NDRs explains each code, such as 5.1.1 (address doesn't exist) or 5.2.2 (mailbox full). Ask the sender to forward the bounce to a personal address you can read.
Check the domain and MX records first
MX records tell the world where to deliver email for your domain. If they are missing or wrong, mail goes to the wrong server or nowhere, even though your mailboxes look fine.
Confirm the domain hasn't expired
Log in to your registrar and check the expiry date. Expired domains stop receiving email within days. Our guide on what to do when a domain expires covers recovery.
Find where your DNS is hosted
Your nameservers decide which company's DNS records are live. This may be the registrar, Cloudflare or your web host. See nameservers vs DNS records if this is confusing.
Look up your live MX records
Use Google's free Admin Toolbox Dig and enter your domain without www. Compare the result with what your email provider expects.
Compare with the correct values
Google Workspace uses one MX record, smtp.google.com, per Google's MX setup page. Microsoft 365 uses a value ending in mail.protection.outlook.com (newer tenants may be given a different host), shown in the Microsoft 365 admin centre under Settings > Domains.
Remove old or extra MX records
Google warns that keeping old MX records can stop email working correctly. Delete any pointing to a previous host or cPanel server.
Trace the message: did it reach your system?
If MX records are correct, check whether the missing message ever arrived. Both platforms keep a log that admins can search by sender, recipient and date.
- Microsoft 365: Exchange admin centre > Mail flow > Message trace. The result shows if a message was delivered, quarantined, failed or filtered as spam.
- Google Workspace: Admin console > Reporting > Email Log Search. It shows whether Gmail received the message and what happened to it.
- No record at all: the message never reached your provider. The problem is on the sender's side or in your DNS.
- Delivered: it reached the mailbox. Look at rules, other folders and forwarding next.
Mailbox full, inbox rules and forwarding
If only one person is affected, look inside their mailbox. Storage limits are a common, quiet cause: Microsoft's Exchange Online limits say that at the prohibit send/receive limit, Exchange Online rejects incoming mail and sends a bounce. Google says a Google Account at its storage limit can't send or receive email in Gmail.
Next, check rules and forwarding. In Outlook, look under Settings > Mail > Rules and Forwarding. In Gmail, check Settings > Filters and Blocked Addresses, and the Forwarding and POP/IMAP tab.
Junk, quarantine and blocked senders
Filters can hold messages where users never look. Microsoft 365 keeps some messages in quarantine rather than Junk; users can review some of them at security.microsoft.com/quarantine, while messages quarantined for high-confidence phishing, malware or mail flow rules are by default visible only to admins. Google Workspace admins can set up admin quarantines in Gmail compliance settings.
Filter and account checks
If the sender is the one being blocked by everyone, not just you, their problem is likely authentication or reputation. Point them to our guide on why emails are not being received by recipients.
Fixes in the right order
Work from the widest cause to the narrowest. Fixing DNS first avoids wasting time on mailbox settings when nothing is reaching the server.
- Renew the domain if expired, and turn on auto-renew with a card that won't lapse.
- Restore correct MX records and remove old ones; wait for DNS to update (Google says up to 72 hours).
- Free up storage or add archive or storage, then ask senders to resend.
- Remove unknown rules and forwarding, reset the password and sign out all sessions if the account may be compromised.
- Release legitimate messages from quarantine and add trusted senders to the allowed list.
- Test by sending from an outside address such as a personal Gmail account.
Do it yourself or get help?
Checking the junk folder, storage and inbox rules is quick. DNS changes and message traces need admin access and some care: a wrong MX edit can stop all email for the company.
Our Quick Fix (1 hour) (S$119) covers a focused fix such as tracing a missing email or correcting MX records. If your DNS is a mess after a website move, our Domain & DNS Setup (S$99) rebuilds the records properly, with email and website pointing where they should.
Frequently asked questions
Most website moves involve changing nameservers to the new host or builder, which replaces your DNS records. If the new DNS zone lacks your Microsoft 365 or Google Workspace MX records, incoming mail goes nowhere. Look up your MX records, add the correct values at the current DNS host, and remove any old ones.
Use a lookup tool such as Google's Admin Toolbox Dig, choose MX and enter your domain without www. Google Workspace should show smtp.google.com. Microsoft 365 should show the host given in the admin centre under Settings > Domains, usually ending in mail.protection.outlook.com. Anything else means mail is going elsewhere.
Yes. Microsoft says Exchange Online rejects incoming mail and sends a non-delivery report when a mailbox reaches its prohibit send/receive limit. Google says an account at its storage limit can't send or receive email in Gmail. Delete large old messages, empty deleted items or add storage, then ask senders to resend.
Check Junk or Spam, Microsoft 365 quarantine and your blocked senders list. Then run a message trace or Email Log Search for their address. If there is no record, the message never left their system or was rejected, so ask them for the bounce message and its error code.
Often within an hour, but Google says MX changes can take up to 72 hours to be recognised across the internet, depending on the old record's TTL and caching by other mail servers. Sending servers usually retry for a period, so some delayed messages may still arrive once the records update.