If you send a mail to a candidate, then you can change the text of the e-mail before you send it. However, if you send an e-mail to a list of candidates you can't change the text.
Carerix differentiates e-mails that are sent from a detail screen and those that are sent from a list.
An e-mail that is sent from a detail screen is always just one message. You can always change this message before you send it.
An e-mail from a list can be meant for multiple recipients. This depends on the amount of users you've selected.
Because you've probably selected multiple recipients when you use a send list template, Carerix will always lock the text because most of the time the text in the e-mail is personalized (example: Dear *Name of the recipient*). If you would change the e-mail, this process would be disrupted.
To be able to edit - parts of - the e-mail before sending you need to use the double bracket method. By adding double brackets you create 'holes' in the e-mail where you need to add text.