First make a file with the name ie. newincommail.txt
Now you can make a new filter with the Action 'Extract' or 'Append' (more than one mail to the same file).

Hallo,

I am a new user of this email client. I decide to use this email client instead of MS Outlook because I want to use some script files wrote in PHP and it seems for better (for me better) understanding of rules, but now I have a little bit problem here, so ...

I need to save content of incoming email to .txt file, but in filter create window there is no any option like this, is it possible create rule for this email content save? Thank you everybody for helping me.