Fix Outlook Error 0x800CCC0E - Cannot Synchronize Subscribed Folders

Outlook stops receiving mail and shows a send/receive error like this:

Task 'Synchronizing subscribed folders for user@gmail.com.' reported error (0x800CCC0E):
'Outlook cannot synchronize subscribed folders for user@gmail.com.
Error: Cannot connect to the server. If you continue to receive this message,
contact your server administrator or Internet service provider (ISP).'

0x800CCC0E means Outlook could not connect to the mail server. It is a connection failure, not a mailbox problem — which is why deleting messages, compacting folders, or repairing your mailbox achieves nothing. Work through the causes below in order; they are ordered by how often they are actually to blame.

Fix 1: Stale OAuth Credentials (Gmail and Yahoo)

Microsoft documented a specific known issue affecting classic Outlook for Microsoft 365: some Gmail and Yahoo accounts stopped syncing as of 26 February 2026, and accounts could also stop syncing after a password change. The reported symptoms were exactly these codes:

Task 'Synchronizing subscribed folders for username@gmail.com.' reported error (0x800CCC0E)
Check for new mail reported error (0x800CCC0E)
Sending reported error (0x800CCC0F)

Microsoft's stated cause was that Outlook was not prompting users to sign in and refresh their credentials, so the stored token went stale and connections failed. Microsoft marked the issue fixed by a Microsoft 365 service change on 20 March 2026.

If you are still seeing it — most likely after a password change — force Outlook to re-authenticate:

1. Close Outlook completely.
2. Open Credential Manager (search for it in the Start menu) and select Windows Credentials.
3. Find entries beginning with MicrosoftOffice16_Data:OAUTH2 that relate to the affected Gmail or Yahoo account.
4. Remove those entries.
5. Reopen Outlook and sign in when prompted.

Outlook recreates the credential automatically, so nothing is lost. Note that after a password change, the old OAuth token can take up to about an hour to expire before Outlook prompts for a new sign-in.

Also check the Google consent screen. During the Google sign-in flow, the permission covering reading, composing, sending, and deleting Gmail messages must be granted to Microsoft apps and services. If that box is left unchecked, Outlook cannot synchronise and reports this same code. Review what you have granted at your Google account's third-party access settings and re-run the sign-in, ticking the permission.

Fix 2: Verify Server and Port Settings

A wrong port or the wrong encryption type produces 0x800CCC0E instantly. Go to File > Account Settings > Account Settings > (select account) > Change > More Settings > Advanced.

If you use POP rather than IMAP, incoming is port 995 with SSL/TLS.

On the Outgoing Server tab, ensure "My outgoing server (SMTP) requires authentication" is ticked and set to use the same settings as the incoming server. Then use Test Account Settings — it tests send and receive separately, which tells you immediately whether the failure is inbound, outbound, or both.

Fix 3: Rule Out Antivirus and Firewall Interference

Security suites that scan email sit in the middle of the IMAP and SMTP connections and can break the TLS handshake outright.

1. Temporarily disable email protection or mail scanning in your security product (not the whole product if you can avoid it).
2. Run Send/Receive All Folders (F9).
3. If the error disappears, re-enable protection and add an exception for Outlook rather than leaving the feature off.

Corporate firewalls and web filters can do the same thing on a larger scale, which is worth knowing before you spend an hour on client settings for a problem that lives on the network.

A useful cross-check: if OneDrive on the same machine is also refusing to sign in with error 0x8004de40, the fault is almost certainly shared TLS or interception at the network layer rather than anything specific to Outlook, since both clients depend on the same Schannel configuration and trusted roots.

Fix 4: Check for Network-Level Blocking

Many consumer ISPs block outbound port 25, and some block 587, to limit spam relaying. Corporate networks often restrict the same ports.

The fastest test is to connect the machine to a mobile hotspot and try Send/Receive again. If it works on the hotspot and fails on your normal network, the problem is network filtering and no Outlook setting will fix it. Either switch to port 465 with SSL/TLS if your provider supports it, or take it up with whoever runs the network.

Fix 5: Rebuild the Local Data File

If a single account on a single machine is affected while the same account works elsewhere, the local IMAP data file may be damaged.

1. Note the file location under File > Account Settings > Data Files.
2. Close Outlook.
3. Rename the account's .ost file — for example to account.ost.old.
4. Start Outlook. It rebuilds the file from the server.

This is safe for IMAP and Exchange accounts because the mail lives on the server. It is not safe for anything stored only in a local PST — back those up first.

Fix 6: Create a New Outlook Profile

This rebuilds the account configuration, the credential reference, and the data file together.

1. Control Panel > Mail (Microsoft Outlook) > Show Profiles > Add
2. Create a new profile and add the account.
3. Set Prompt for a profile to be used so you can switch back if needed.

Keep the old profile until you have confirmed the new one works.

Verify the Fix

• Press F9 (Send/Receive All Folders) and confirm no error appears in the Send/Receive Progress dialog.
• Send yourself a message and confirm it arrives — this exercises both SMTP and IMAP.
• Check File > Account Settings > (account) > Test Account Settings for two green ticks.
• If Outlook is running, hold Ctrl and right-click the Outlook icon in the notification area to reach Connection Status, which shows live server connections.

Prevention

• When you change your Gmail, Yahoo, or Microsoft account password, expect Outlook to need a re-authentication and allow up to an hour for the old token to expire.
• Do not revoke Microsoft's access in your Google account's third-party permissions unless you intend to stop using Outlook with that mailbox.
• Keep Outlook updated — several sync failures in this family were fixed on the client and service side rather than by anything you can configure.
• If you administer mailboxes, see our guides on configuring email forwarding in Office 365 and granting a user access to another mailbox.