Logging SMTP session, including message text

I’m trying to chase down a problem between Thunderbird and a specific mail server. I need to see the actual message text being sent to the server. setting NSPR_LOG_MODULES=SMTP:5 shows me the SMTP commands being sent, but it doesn’t include the actual message text.

Is there a way to include the message text?

I’m using TBird 91.4.1 64 bit on Windows 10 x64.