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Outgoing Authentication Issues? - Check Email Logs

Very Insightful Person
Very Insightful Person


There have been a number of threads on the boards lately where people have been seeing the password prompt pop up when trying to send e-mails.

While the symptom is the same for many users, there are actually a number of possible causes.

Broadly speaking they fall into two categories.

1. Username/Password incorrect - The server sends a 535 Authentication details invalid
2. Authentication refused for other reasons - The server sends 525 Authentication denied

To find out more it's necessary to turn on E-Mail logging in a mail client and view the logs to see which error was returned.

The aim of this post is to show how to turn on logging in 2 popular email applications.

Microsoft Outlook
Mozilla Thunderbird

Unfortunately mobile clients such as those in the Iphone and Android phones don't come with an easy option to do this.  And while Windows Live Mail does include a logging option.  I personally find more and more reasons NOT to use Live Mail.


When posting logs post as little as possible - as a rule it's only necessary to post the actual Authentication results line.

Outlook and Thunderbird both hide the password used in the logs, but a number of people who've posted logs from other sources in the past have actually posted their email address and password.

For Example


auth login
334 VXNlcm5hbWU6
334 UGFzc3dvcmQ6
235 ... authentication succeeded

All that's needed is the line in green IN FULL - in this case a successful send.


NEVER POST THE LINES IN RED without changing them.  They are your email address and password.  They are not encrypted.

To find my address and password just paste the lines in red individually here and press decode.

Microsoft Outlook

To turn on logging in Outlook do the following.

  1. Click File->Options
  2. Click Advanced on the left side of the options panel
  3. On the right side scroll down to other and click Enable troubleshooting logging (requires restarting outlook)
  4. Click ok then close Outlook
  5. Re open Outlook and try sending a mail.
  6. Go back into options and turn off logging.

Note when logging is enabled you will get a warning when you start Outlook.  clicking the warning will automatically turn off logging if you forget to do step 6 but the change will only take effect after Outlook has been closed.

To find the log file in Outlook 2016 do the following.

  1. Open File Explorer
  2. In the address bar type "%TEMP%\Outlook Logging" and press Enter
  3. Double click Opmlog.log
  4. The file will open in Notepad look for the following lines
    2016.10.11 20:06:43 SMTP ( [tx] AUTH LOGIN
    2016.10.11 20:06:43 SMTP ( <rx> 334 VXNlcm5hbWU6
    2016.10.11 20:06:43 SMTP ( [tx] <base 64 username>
    2016.10.11 20:06:43 SMTP ( <rx> 334 UGFzc3dvcmQ6
    2016.10.11 20:06:43 SMTP ( [tx] *****
    2016.10.11 20:06:43 SMTP ( <rx> 235 ... authentication succeeded
  5. As noted earlier we only need to see the line in green.

Mozilla Thunderbird

Using information from here - I've created a batch file to start a special session of Thunderbird with logging turned on for SMTP.

Things to note:

  1. The file makes no permanent changes to Thunderbird.  The variables that turn on logging only work for the duration of the batch file.
  2. Wherever the batch file is run from  it looks for and if necessary creates a single folder tbirdlog in order to store the log file.  It then sets the variables to turn on logging and starts thunderbird.


@echo off
REM Check if there's a log folder already created
if exist %~dp0tbirdlog goto continue

REM If not then create it
echo creating log folder %~dp0tbirdlog
md %~dp0tbirdlog

REM Set logging environment variables
set NSPR_LOG_FILE=%~dp0tbirdlog\tbird.log

start thunderbird

Setting up

  1. Open Notepad
  2. Copy the above text into notepad and click save as
  3. Choose the location you wish to save.  The bat file can be run from anywhere.  I have mine on my Desktop
  4. Change the Save as Type to All Files (*.*) And type tbirdlog.bat as the filename
  5. Click Save

Go to the location you've stored the file and double click it.  

The first time it's run you'll see a folder tbirdlog appear in the same folder as the bat file,  The command window will close and Thunderbird will start up.

Try sending and close Thunderbird in order to save the log file.

Double click the tbirdlog folder to open it and double click tbird.log to open the file in notepad.

This time were looking for the following lines.

19720[1511140]: PLAIN auth
19720[1511140]: Logging suppressed for this command (it probably contained authentication information)
19720[1511140]: SMTP entering state: 0
19720[1511140]: SMTP Response: 235 ... authentication succeeded

Again the main thing we need is the line in green.

Note: The bat file is 100% safe.  I've put in a lot of time helping out on this board as a Superuser.  I have no intention of ruining all that good work by distributing files that will damage anyone's systems.  It makes no changes to the Thunderbird installation.  I do intend to modify it to add timestamps as currently it overwrites the previous log file when run.  But I will leave the original up if I do so.


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