Is it possible the use of custom fields when posting via email?

Yes, but it depends on which form plugin you’re using. With which plugin are you trying to do this?

Hi, Steve. Thanks for your reply.
I would like to do it without using any plugin; directly activating the option from wordpress: Settings ? Writing : Post via e-mail.

• This reply was modified 4 years, 10 months ago by romiri.

post via email is for sending an email to your site to create a post. Enabling that is dangerous. Just sayin’. See https://jetpack.com/support/post-by-email/

Ok. Thanks a lot for the information. So, better I don’t use that option…