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License Error 0x8004210A

Send/Receive Timeouts 0x8004210A and 0x8004210B: Outlook Gives Up Waiting on Server

11 min read Updated October 5, 2026 Outlook & Office Applications

Fix it now

Outlook gave up waiting. A connection was made, which is what separates these from the connection failures, and then the reply did not arrive in time. Almost always something in the path is holding the data rather than blocking it, so find out whether the transfer completes slowly before you start changing timeouts.

  1. Turn off your security product’s email scanning component – that component only – and run one full send and receive. If the delay disappears, you have the answer without changing anything in Outlook.
  2. If it still stalls, raise the server timeout: File, Account Settings, open the account, More Settings, Advanced, and move the Server Timeouts slider up. Run the cycle again.
  3. Read the result carefully. If it now completes but slowly, something is buffering the transfer and the timeout was hiding it. If it fails at exactly the same point regardless, one specific message is at fault.
  4. Rather than leaving scanning off, add the vendor’s documented exclusions for the Outlook data file folder and the Outlook process, and disable the product’s POP3, IMAP and SMTP proxying specifically.
  5. Test on a different network before you conclude anything, because a slow, contended or lossy link produces the same failure with no scanner involved.

Put the timeout back once you know the cause. A mailbox that needs the maximum every day has a problem that is being hidden rather than fixed.

If a full cycle completes, including a message with a large attachment, you are done. If not, the next section explains what the timeout is actually timing.

Why it happens

Microsoft publishes no meaning for 0x8004210A, 0x8004210B, 0x80042108 or 0x80042109. The common reading – two of them are timeouts on the incoming and outgoing server, two are connection failures on the same pair – is inference rather than documentation. It is a reasonable working model and this article uses it, but it is not something to spend money on.

What matters more is what the timeout actually measures. The server timeout in Outlook is not a limit on how long a send and receive may take. It is how long Outlook will wait for the server to respond to a step in the conversation. A very large attachment can take several minutes to transfer without ever tripping it, because data keeps arriving and the wait keeps resetting. What trips it is silence.

That is why a local mail scanner is so often the cause. It accepts the connection from Outlook, fetches the whole message itself, scans it, and only then starts passing it on. From Outlook’s point of view nothing at all arrives for the entire duration of that scan. On a large message, a slow machine, or a scanner that is itself waiting on something, the silence outlasts the timeout and the session is abandoned. The message is still on the server, so the next cycle starts the same doomed download again.

Seeing connection failures and timeouts alternating on the same account is normal and does not mean you have two problems. It means one unreliable path failing at whichever stage it happens to reach that time. Chasing them as separate faults is how a single afternoon’s problem becomes a week’s.

A mail scanner is buffering the whole message before releasing it

You have this one if Everything works with the mail scanning component disabled, and large messages are the worst affected.

  1. Disable the POP3, IMAP and SMTP scanning component specifically, leaving file-level real-time protection running.
  2. Add the vendor’s documented exclusions for the Outlook data folder and the Outlook process.
  3. Retest with a message carrying a large attachment rather than a small test message.
  4. If the product re-enables the component after an update, look for a policy setting rather than fixing it locally each time.

Scanning the mail stream at the socket adds little on a machine that already scans files as they are written and opened, where the mail service filters messages before they arrive. It is the component most worth switching off.

The link is genuinely slow and the timeout is at its default

You have this one if Failures are consistent on a slow or heavily contended connection, and webmail is sluggish on the same machine.

  1. Raise the Server Timeouts slider towards the top of its range while you diagnose.
  2. Increase the interval between automatic send and receive cycles so a slow cycle is not overtaken by the next one.
  3. Do the first large synchronisation on a faster connection where you can.
  4. Put the timeout back afterwards, so the next problem is visible rather than absorbed.

One oversized or damaged message is blocking the queue

You have this one if The failure happens at the same point every attempt, and the count of undownloaded messages on the server never falls.

  1. Sign in to webmail and find the oldest message that has not reached Outlook.
  2. Open it there and save anything you need from it, because Outlook never received a copy.
  3. Delete it and empty the deleted items folder so the server stops offering it.
  4. Return to Outlook and run a send and receive; the queue should move on.

Too many accounts or send and receive groups running at once

You have this one if A profile with several accounts times out on all of them at roughly the same moment.

  1. Open Send/Receive, then Send/Receive Groups, then Define Send/Receive Groups.
  2. Stagger the schedules so groups do not overlap, and give a heavy account a group of its own.
  3. Remove accounts nobody uses any more; each one costs a connection on every cycle.

The path itself is lossy rather than slow

You have this one if Timeouts and connection failures alternate on the same account, and the same machine behaves differently on another network.

  1. Test on a phone hotspot to take the local network out of the picture entirely.
  2. If the hotspot is reliable, the fault is the network rather than Outlook or the mailbox, and it belongs with whoever runs it.
  3. Check whether a VPN is in the path, because it changes both the route and what inspects the traffic.

Full reference

Matching the pattern to the cause

Symptom Where the fault is
Small messages fine, large ones time out Something is buffering the transfer, usually a scanner or a slow link
Times out at the same point every attempt One specific message at the head of the queue
Only on one network Bandwidth, latency or packet loss on that link
Only since a security product was installed or updated Its mail proxy
Both sending and receiving time out The path or the machine rather than the mailbox
Timeouts and connection errors alternating One unreliable path, not two problems

Raising the timeout without hiding the cause

  1. Note what the timeout is set to now, so you can put it back.
  2. Raise it to the top of the range as a diagnostic, not as a fix.
  3. Run a full cycle and record whether it completes and how long it took.
  4. If it completes, you have proved the transfer works and something is delaying it – now go and find that.
  5. If it fails at the same point regardless of the timeout, the timeout was never the constraint and one message is.
  6. Return the setting to its original value once you know which of those two it is.

If you delete a blocking message on the server, it is gone – Outlook never received a copy. Open it in webmail and save the attachments and the text you need before you delete anything, and be particularly careful where the mailbox is the only place that mail exists.

What to exclude, and what not to

  • Exclude the folder holding the Outlook data files, and the Outlook process itself, according to your vendor’s documented list.
  • Disable the mail proxying component specifically. Turning the whole product off to test is fine; leaving it off is not.
  • Do not exclude the entire user profile folder to save time. That is a much larger hole than the problem justifies.
  • Check whether the setting survives an update. Products that re-enable a component on upgrade need a policy rather than a local change.
  • Where the mail service already filters messages before delivery, socket-level scanning is duplicating work that has been done twice already.

When it is the mailbox rather than the path

These codes are about a step in a conversation, not about the size of the local store, so a large mailbox on its own does not cause them. What can is a mailbox with a very large single item at the head of a POP queue, or an account that has been offline long enough that the first cycle after reconnecting tries to move a great deal at once. In the second case the fix is patience and one uninterrupted cycle, on the best connection you can find, rather than any setting.

It is worth checking whether the account should be POP at all. A protocol that works through one ordered queue turns a single oversized message into a total stoppage; one that synchronises folders does not. That is a design decision rather than a repair, but if this is the second or third time, it is the decision worth making.

When a licence is the actual fix

Turning off the mail proxying component costs nothing and is the correct first move, so start there – and on a single machine, removing a third-party suite in favour of what Windows already includes is a legitimate and free answer. This becomes a purchasing question only for an estate running an expired or consumer-grade product whose mail scanner cannot be disabled centrally, keeps returning after updates, and is slowing every mailbox in the building. Arco supplies business antivirus licences from the main vendors and can tell you which of them scan mail at the socket and which rely on file-level scanning plus server-side filtering, so you can choose one that stays out of every send and receive.

Every code this article covers

Code What it points at Source
0x8004210A Seen when a send and receive gives up waiting for the server. No published meaning; commonly read as the incoming server, and diagnosed by whether the transfer completes when the timeout is raised not published by the vendor
0x8004210B Seen in the same circumstances, commonly read as the outgoing server. No published meaning not published by the vendor
0x80042108 Seen where Outlook could not connect rather than timing out, commonly read as the incoming server. No published meaning not published by the vendor
0x80042109 Seen in the same circumstances, commonly read as the outgoing server. No published meaning not published by the vendor

Confirm the fix worked

  1. A full send and receive completes with no timeout.
  2. A message with a large attachment both leaves and arrives.
  3. The security product’s remaining components are back on, with exclusions in place, and mail still flows.
  4. The message count in webmail matches what Outlook holds, so nothing is stuck behind.
  5. The server timeout is back at its original value and the cycle still completes, which is what proves the cause was fixed rather than absorbed.

Questions people ask about this

How high should I set the timeout?

Put it near the top of the range while you diagnose, so you can see whether the transfer completes at all, then put it back. Leaving it there is harmless but hides the real cause, and a mailbox that needs the maximum every day has a problem worth finding.

Does this mean my mailbox is too big?

Not directly. These codes are about a step in a mail conversation, not about the size of the local store. A single very large message will do it; a large mailbox on its own will not.

Is it risky to turn off email scanning in my antivirus?

The risk is modest on a properly managed machine. Attachments are still scanned when written to disk and when opened, and mail services filter messages before they reach you. Scanning the stream at the socket duplicates work already done elsewhere.

Do I need to buy different antivirus software to fix this?

Usually not. Disabling one component in the product you already have is free, and on a single machine so is removing it in favour of what Windows includes. A licence purchase only makes sense where you need central control over machines you cannot configure individually.

Are these codes documented anywhere?

Not by Microsoft. The incoming and outgoing split you will see quoted is inference. It is a useful working model – just do not treat it as evidence when you are deciding whether to replace a product.

Related error codes

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