I am configuring an IMAP mailbox backup for multiple user accounts, but some accounts fail during authentication while others connect successfully. All accounts are accessible through their respective webmail interfaces, so I am trying to identify whether the issue is related to IMAP configuration, authentication policies, or server-side connection restrictions.

This is becoming difficult to troubleshoot because the accounts belong to different users and may have different security settings. Some providers require OAuth 2.0, while others may require app passwords or specific IMAP access permissions. I do not want to disable security controls across the organization just to complete an email archive.

I am trying to understand a few technical points:

• How can I verify whether IMAP access is enabled for each mailbox?

• Which server address, port, and encryption settings should be checked before connecting?

• How should accounts using OAuth 2.0 or app passwords be handled?

• Can connection failures caused by incorrect credentials be distinguished from server timeouts or blocked ports?

• What should I check if authentication succeeds in webmail but fails through an IMAP client?

• Is there a recommended way to test one account before processing a CSV list of multiple mailboxes?

I found the SysInfo IMAP Backup Tool, which supports IMAP account backup and CSV-based batch processing. I am considering testing a few accounts individually before running the complete job. I would also review the application's processing report to identify accounts or items that were skipped or failed.

I understand that successful webmail login does not necessarily confirm that IMAP access is enabled or that the account permits third-party connections. I would prefer to diagnose the authentication method and server configuration first rather than repeatedly retrying the same credentials.

For administrators who have handled bulk IMAP backups, what is your preferred troubleshooting sequence for authentication failures across different providers? Are there particular server-side settings or logs that help identify the root cause?

Thank you, very useful information.