smtp problems: can i log sessions?

Hi,
I'm having serious problems in sending email with TB portable.
I've been using it since January but in the last month I got the evidence that some mails I sent never reached destination.
I contacted my smtp provider (i rely on it independently of the network I'm connected to) who replied me saying that such emails never traveled on the smtp server, however TB placed those emails in the "sent" folder without giving me any kind of error message.

I want to log the smtp session (and also imap/pop3) of TB and check if I can understand what happens and why TB seems sending the email but in reality it doesn't happen (for info: i've 14 email account managed on TB portable, and 2 smtp server)

Following mozillazine instructions, I created the batch file: mozilla.bat

SET NSPR_LOG_MODULES=POP3:4
SET NSPR_LOG_MODULES=IMAP:4
SET NSPR_LOG_MODULES=SMTP:4
SET NSPR_LOG_FILE=g:\email\log\logfile.txt
start ThunderbirdPortable.exe

But the logfile is always zero byte long.
Is it possible to log sessions with portable TB?
Thanks in advance.
Paolo