Windows  ·  high  ·  Microsoft Office

Send and receive errors — 0x800CCC0E, 0x8004210A, 0x800CCC0F

Mail stops moving and the send/receive dialog reports a connection error. These codes all mean the same class of thing — Outlook could not complete a conversation with the mail server — and the useful work is finding out which hop failed.

What you see

Mail sits in the outbox, or the send/receive progress window shows "Task reported error (0x800CCC0E)" or "The operation timed out waiting for a response". Webmail for the same account works, which is what tells you the mailbox itself is fine.

What is actually wrong

Four things produce these, in rough order of likelihood: security software intercepting the mail connection, the wrong port or encryption setting on a manually configured account, a network path that blocks the port outright, and a very large message stalling the connection until it times out. 0x800CCC13 is the odd one out and usually means damaged system files rather than a network problem.

Codes and articles

0x800CCC0E0x8004210A0x800CCC0F0x800CCC130x80042109Task reported erroroperation timed out

Start here — find out which fix applies

A script that runs the 3 inspection commands from the write-up below and prints what each one returned. It reads the machine and changes nothing — every command that could write, delete, start or stop is excluded from it by construction. Run this first, then pick the fix its output points at.

Download the read-only diagnosticchanges nothing · safe to run before reading

Fixes (4)

Clear a message that is jamming the queue
Outlook, as the affected user20 minuteslow riskreversible

Check this before anything technical. One oversized message in the outbox stalls every send behind it and produces a timeout that looks exactly like a network fault.

  1. Work offline first, so Outlook stops retrying while you are in the outbox. Send/Receive → Work Offline.

    Without this, Outlook locks the message it is trying to send and you cannot delete or move it. This is why the outbox appears impossible to clear.

  2. Open the Outbox and sort by size. Anything above about 20 MB is likely to be the problem — most mail systems reject or stall well below the limit they advertise.

  3. Drag the oversized message to Drafts, remove the attachment, and send the attachment another way — a OneDrive or SharePoint link is the intended route.

  4. Go back online and let the queue drain. Send/Receive → Work Offline again to toggle it off.

  5. If the outbox still will not clear, check for a message with no recipient or a corrupted one, which sticks in the same way.

Confirm it workedThe outbox empties and new mail sends within a few seconds.
If you need to undo itNothing was deleted — the message is in Drafts. Nothing to reverse.
Rule out security software intercepting the connection
PowerShell as administrator30 minutesmedium riskreversible

An Exchange or Microsoft 365 account that was working and stopped, especially after a security product was installed or updated.

  1. Check whether the machine can reach the service at all.

    PowerShell
    Test-NetConnection outlook.office365.com -Port 443 | Select-Object ComputerName, RemoteAddress, TcpTestSucceeded

  2. Look at what certificate is actually being presented. An interception proxy substitutes its own.

    PowerShell
    $c=[Net.Sockets.TcpClient]::new('outlook.office365.com',443)$s=[Net.Security.SslStream]::new($c.GetStream(),$false,{$true})$s.AuthenticateAsClient('outlook.office365.com')$s.RemoteCertificate.Issuer

    If the issuer is Microsoft, the connection is reaching Microsoft. If it names your antivirus or a firewall vendor, the mail traffic is being decrypted and re-signed in transit — which is the single most common cause of these codes on an otherwise healthy machine.

  3. Turn off the mail-scanning component specifically — not the whole product — and test. Most products have a separate "scan outgoing/incoming mail" or "SSL scanning" switch.

  4. If that fixes it, add the Microsoft 365 endpoints to the product's exclusion list rather than leaving mail scanning off. Vendors publish these lists and Microsoft documents its own endpoints.

  5. Re-enable everything you turned off, once the exclusion is in place.

Confirm it workedMail sends and receives with the security product fully enabled and the exclusion applied.
If you need to undo itRe-enable any component you disabled. Leave nothing off at the end of this — the diagnosis is the point, not the workaround.
Download this fix as a PowerShell scriptneeds an elevated shell · 3 steps you do yourself · asks before each step
Correct the server, port and encryption settings
Outlook account settings, as the affected user30 minuteslow riskreversible

A POP or IMAP account set up by hand, or an account that fails only when sending.

  1. Confirm the machine can reach the SMTP port the account is configured for.

    PowerShell
    Test-NetConnection smtp.yourprovider.com -Port 587 | Select-Object RemoteAddress, TcpTestSucceeded

    A failure here and not on 993 or 995 is why receiving works and sending does not. Many networks and most consumer ISPs block outbound port 25 to stop spam, so an account configured for 25 will receive perfectly and never send.

  2. Open File → Account Settings → Account Settings → the account → Change → More Settings → Advanced, and compare against what the provider publishes. The usual current values are 993 with SSL/TLS for IMAP, 995 with SSL/TLS for POP, and 587 with STARTTLS for SMTP.

  3. On the Outgoing Server tab, confirm "My outgoing server (SMTP) requires authentication" is ticked. An unauthenticated SMTP submission is refused by every current provider.

  4. Raise the server timeout on the Advanced tab to 5 minutes if the connection is slow or the mailbox is large.

    0x8004210A is literally a timeout. The default is one minute, which a slow link or a large first sync will exceed.

  5. If the provider has moved to modern authentication, a manually configured POP or IMAP account with a plain password will now be refused regardless of ports. Remove it and let autodiscover set the account up instead.

Confirm it workedSend/Receive completes with no error, and a test message to yourself arrives.
If you need to undo itNote the previous values before changing them; put them back if the change does not help.
Download this fix as a PowerShell script4 steps you do yourself · asks before each step
Test the network path properly
PowerShell as the affected user30 minuteslow riskreversible

Nothing above applies, or the fault follows the machine between networks — or does not.

  1. Establish whether the network is the variable by testing on a different one — a phone hotspot is the quickest.

    This one test splits the problem in half. Working on a hotspot and failing on the office network means the fault is the network, not Outlook, and everything you would have done to the client is wasted effort.

  2. Check name resolution is returning something sensible.

    PowerShell
    Resolve-DnsName outlook.office365.com | Select-Object Name, Type, IP4Address -First 5

  3. Check whether a proxy is configured that mail traffic is being forced through.

    PowerShell
    Get-ItemProperty 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings' | Select-Object ProxyEnable, ProxyServer, AutoConfigURL

  4. Run Microsoft's own connectivity test against the account, which checks the whole path from outside and reports which hop failed.

    PowerShell
    Start-Process 'https://testconnectivity.microsoft.com/'

  5. If the office network is the variable, take the findings to whoever runs the firewall. Mail inspection appliances and SSL-inspecting proxies are the usual cause and it is not fixable from the client.

Confirm it workedSend/Receive completes on the network that was failing.
If you need to undo itNothing changed on the machine — this fix is diagnosis only.
Download this fix as a PowerShell script2 steps you do yourself · asks before each step

Related faults

Outlook keeps asking for a password and will not accept itWindowsIntermittent connection failures where IPv6 is half-configuredWindowsOutlook search returns nothing, or misses recent mailWindows"Cannot start Microsoft Outlook. Cannot open the Outlook window"WindowsAn add-in keeps disabling itself, or will not stay enabledWindowsOutlook cannot set up the account, or connects to the wrong serverWindows

Where this stops. This write-up was written and checked by hand. It says what each step changes, how to confirm it worked and how to reverse it, and anything destructive is flagged before you reach it. If it does not match what your machine is doing, search the Support Centre for the exact code or message — and when something needs a person, get in touch.