What is your anti-virus software?

I have also heard there is so called self-destructive e-mails

Not in Thunderbird.

how are these done ??

Not sure what exactly you heard. I doubt there are self-destructing emails at all.

Freezing the thunderbird will only happen with this senders e-mails. Not even depending upon the size. So there must be something in the mail.

Self-destruct mail I have heard from trusted person who claimed that he had a telephone number by mail saying that write down the number now as the mail will destroy itself...could this be some apple etc. Application...

Please forward me an example of the offending email. Send it as an attachment.

xenos at gmx dot co dot uk

For malicious code to do something it has to be evaluated or executed. Thunderbird does not run the type of script (javascript) that can be embedded in email.

I'd suspect this message has many links to content on a slow-responding server.

I think your "trusted person" may mean well but I believe his advice is misleading.