To remove an existing header the below setting can be added to the [general] section of the account#/config/general.config file. It should contain a comma-delimited list of header names to remove. Below is an example.
HeadersToRemove=Date,Subject
To add a new header the below setting can be added to the [general] section of the account#/config/general.config file. It should contain a "rn" delimited list of header names and values to add. Below is an example.
HeadersToAdd=x-mailer:mymail 1rnx-sender:mysender.com
To modify an existing header the below setting can be added to the [general] section of the account#/config/general.config file. It should contain a "~:~" key value pair list that is delimited by ~,~. Below is an example.
HeaderValuesToReplace=bob@olddomain.com~:~bob@newdomain.com~,~^From:~:~ReplyTo: