Share via

Enable transport logging in Outlook

  • Article
  • Applies to:
    Outlook for Microsoft 365, Outlook 2021, Outlook 2019, Outlook 2016

Microsoft Outlook supports logging the communications that occur between Outlook and various types of email servers. These logs can be helpful when you troubleshoot problems that affect the transfer of messages between Outlook and the email server.

Outlook can log its communications with Microsoft Exchange, Post Office Protocol version 3 (POP3), Simple Mail Transport Protocol (SMTP), Internet Messaging Access Protocol (IMAP), and Outlook.com servers.

Enable logging

Use the following steps:

  1. On the File tab, click Options.
  2. In the Outlook Options dialog box, click Advanced.
  3. In the Other section, select the Enable troubleshooting logging (requires restarting Outlook) check box, and then click OK.
  4. Exit and then restart Outlook.

Logging results

Important

This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For protection, back up the registry before you modify it so that you can restore it if a problem occurs. For more information about how to back up and restore the registry, see How to back up and restore the registry in Windows.

When you enable logging, the following registry key is configured:

Subkey: HKEY_CURRENT_USER\Software\Microsoft\Office\1x.0\Outlook\Options\Mail

DWORD: EnableLogging

Values: 1 = logging enabled, 0 = logging disabled

Note

In the subkey, <1x.0> represents the program version number. "16.0" denotes Outlook 2021, Outlook 2019, Outlook 2016 or Outlook for Microsoft 365.

After you enable logging, all communications that occur between Outlook and the email server are written to a log file.

Important

You must disable logging after the logs capture the failed communication to the server. If you don't disable logging, the logs will grow indefinitely.

Log file locations

The log files are formatted as plain text.

POP3, SMTP, MAPI logs

The POP3, SMTP, and MAPI transport types are written to a single log file in the following location:

%temp%\Outlook Logging\Opmlog.log

IMAP logs

The IMAP transport type is written to the following location:

%temp%\Outlook Logging\IMAP-usernamedomainname-date-time.log

For example: IMAP-user1wingtiptoyscom-03_23_2014-12_49_31_798.log