Canon/MP Navigator EX
I'm the resident computer wizard for my extended family. One setup has a Canon scanner and I ran into this problem after I converted their mail account from <gasp> Outlook Express 6.0 to Mozilla Thunderbird due to UTF-8 issues with mails.
One nice day I got a call telling me that the Scan to Mail function of the MP Navigator EX software was no longer working correctly. The Thunderbird forum in German had the solution. But this can be applied to any other mail client that is registering itself under the HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail.
Fire up regedit.exe and navigate to the HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail key it should look somewhat like the below.
HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail Hotmail Mozilla Thunderbird Outlook Express
For our purpose we want to use Mozilla Thunderbird which is not listed in MP Navigator EX yet.
Next open explorer and navigate to %ProgramFiles%\Canon\MP Navigator EX 5.0\Device\ mg6200.ini
[Application] Mailer0=Outlook Express Mailer1=Microsoft Outlook Mailer2=Windows Mail Mailer3=Windows Live Mail Mailer4=Mozilla Thunderbird
[Application] Mailer0=Mozilla Thunderbird Mailer1=Microsoft Outlook Mailer2=Windows Mail Mailer3=Windows Live Mail ;Mailer4=Outlook Express