Issue when using an external SMTP email server for the internal emails

Hey guys! I am currently using an external mail server for the internal emails, but for some reason the internal emails are being sent without a sender header. I used the [] script for the setup.

And for some reason cron jobs messages are sent with the email [[email protected]] instead of the externally set email [[email protected]]. (My external mail server therefore refuses to send these emails)

Anyone know why this might be happening?