Edit mail sending headers

Where can i find and edit the script that controls the headers of the mail system setup on easyengine stack

What do you want to achieve?

My mails are failing to yahoo addresses because the subject field is passed twice. I want to remove one

Any thoughts? @SaskiaLund

Hm… Are you sending those Emails via SMTP? Via Roundcube GUI? Php mail function on your website?

Via Roundcube GUI

@SaskiaLund any ideas?