Try following variations:

&attachment or &attachments instead of &attach. These are some variations I saw with quick googling. Also, original mailto rfc document doesn’t have any notion of attachments. Those were added later as a part of MIME extentions.

It doesn’t run.

If would be possible find another solution even mailto should be ok for me.

In thunderbird you can use the command line :

thunderbird -compose “to=asd@asd,subject=Prova,body=bodybodybody,attachment=‘file:///C:/logfile.log’”

Link… [kb.mozillazine.org])

stuk’s tip was very helpful for me – thanks to stuk!