By default, MailBul does not allow FROM spoofing, that is, it does not allow you to send email from an address that is different than the FROM address you used in your delivery server settings.
This happens because, most of the delivery servers will reject emails that try to use a different FROM address than the one used for authentication at the server. There are also 3rd-party smtp servers where you have to confirm the email address you are using in the FROM and then if MailBul would allow FROM spoofing, then you’d send from an unverified email address and all your emails will fail sending, so simply put, by default, MailBul plays it safe.
However, in the delivery server, there is a setting called “Force FROM” which by default is set to “Always”. If you are absolutely sure your delivery server allow FROM spoofing, then you can set this option to “Never”. Please beware, if your delivery servers do not support FROM spoofing, all your emails will fail sending and there’s nothing MailBul can do to help. Use with caution.