Migration from IONOS to Microsoft

Pattabiraman Raghuraman 0 Reputation points
2026-09-02T07:19:19.3666667+00:00

We are getting below error. We have corssed checked and IMAP & Login details are all correct.

Status

Data migrated:

Migration rate:

Error: RemoteNetworkErrorTransientException: We were unable to reach your email provider. Please check your server settings, or try again later. --> Connection has shut down. --> A request to send or receive data was disallowed because the socket had already been shut down in that direction with a previous shutdown call.

Last successful sync date:

Data consistency score:

Microsoft 365 and Office | Subscription, account, billing | For business | Other
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  1. Michelle Nguyen 1,510 Reputation points Independent Advisor
    2026-09-02T07:41:57.9966667+00:00

    Hi @Pattabiraman Raghuraman

    Based on the error message, it appears that Microsoft 365 is unable to maintain a stable connection to the IONOS mail server during the migration process.

    At first, could you share:

    • The IMAP server hostname and port being used (you may mask sensitive information).
    • Whether SSL/TLS is enabled.
    • Whether all mailboxes fail or only specific mailboxes.
    • The migration batch error details from the Exchange Admin Center.

    Since you have already verified that the IMAP settings and credentials are correct, I would recommend checking the following:

    • Confirm that the IMAP server is reachable from external networks and is not experiencing a temporary service issue.
    • Verify whether any firewall, IP restrictions, rate limiting, or security policies on the IONOS side could be blocking connections from Microsoft 365 migration services.
    • Ensure that IMAP access is enabled for the mailbox and that the account is not protected by additional authentication requirements that could interfere with migration.
    • Because the exception is marked as Transient, waiting for a short period and retrying the migration may also help if the issue is related to a temporary network interruption.

    If the problem persists, more details may help narrow down whether the issue is related to connectivity, authentication, or a server-side restriction on the source platform.

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  2. AI answer

    2026-09-02T07:19:37.9766667+00:00

    RemoteNetworkErrorTransientException in an IMAP migration usually means Exchange Online could not complete the network connection to the source IMAP server, even if the username, password, and IMAP settings are correct.

    Check these items in order:

    1. Verify the IMAP server FQDN is public and resolves in DNS.
      • This error can occur when the IMAP server name used in the migration endpoint or batch is not publicly resolvable.
      • In the Exchange Admin Center, go to recipients > migration.
      • If creating a batch with no existing endpoint: start Migrate to Exchange Online > IMAP migration and enter the correct publicly resolvable FQDN.
      • If using an existing endpoint: go to ... > Migration endpoints, open the IMAP endpoint, and confirm the FQDN is correct.
      • If the FQDN is wrong or no longer resolves publicly, recreate the endpoint or create a public host (A) record that resolves that FQDN to the IMAP server public IP.
    2. Test connectivity to the IMAP port from outside the source environment.
      • Use Telnet to test port 993 for SSL or 143 for non-SSL: 
             telnet server.contoso.com 993
      • If the connection fails, publish the required port through the firewall or through the provider hosting the IMAP service.
      • A timeout can also happen if the IMAP service itself is not running.
    3. Confirm the source IMAP service is running.
      • If the source system is Exchange Server, open Services.msc and verify Microsoft Exchange IMAP4 is started.
      • If the source system is a third-party provider such as IONOS, confirm with that provider that IMAP access is enabled and reachable externally.
    4. If the migration is using an existing IMAP endpoint, remove and recreate it.
      • In EAC: Recipients > Migration > More... > Migration endpoints.
      • Delete the affected IMAP endpoint.
      • Create a new IMAP endpoint and re-enter the connection settings, including the correct FQDN.
      • The documented default optional values when creating the endpoint are 20 concurrent migrations and 10 incremental syncs.
    5. If the migration starts but is slow or stalls, review per-user status.
      • In EAC: recipients > migration > select the IMAP batch > View details.
      • Check whether affected users show Syncing and whether Items Synced increases after a few hours.
      • If migration is slow, increase IMAP connection limits on the source server, firewall, or provider if that system is under control.
    6. If the issue continues, escalate.
      • Create a support incident with Microsoft Online Services support.
      • If IONOS hosts the source mailbox, also verify with IONOS that their IMAP endpoint is accepting external connections and not rate-limiting or dropping sessions.
    AI-generated content may be incorrect. Read our transparency notes for more information.

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