When the "E-mail from address" option on webform submission e-mails is customized, spam filters may recognize it as spam or as a phishing attack and block the e-mail. This has happened in the wild several times (e.g. DD ticket #1797).
The reason this field is used, is because receivers want to be able to reply to the e-mail without having to copy/paste the e-mail address from the submission data.
I suggest we remove the ability the customize the "From" header to prevent this issue, and instead add the ability to customize the "Reply-To" header instead. This way, the e-mail won't get blocked and can still be directly replied to.