We are running a multi centre study where a number of different admins will be able to send out emails to different groups of participants.
The only contact the participants have with the study is via their local admin - and they will not recognise the email of the survey admin.

In all cases, the user who has permissions to send out emails will typically be the person who has contacts with participants outside of Limesurvey. Given that, it makes more sense if the "from" field is populated from the logged in user rather than the survey admin - for most small projects these will be the same in any case.

I have modified the admin/token/email.php file to achieve this, though I think the very best option would be if this were configurable in the site general options (either survey admin or user logged managing the tokens) - something which is beyond my skills.