Navigate to Menu > Portal Settings > Email Settings:
NowInfinity allows you to customise the outgoing email address for all correspondence to your clients. This article explains the "firstname.lastname@example.org - Default NowInfinity email" option, however there are 2 other options, which are recommended:
Default NowInfinity email
By default, email@example.com is used to send email correspondence to your clients. This is enabled to allow you to begin corresponding via the platform straight away. We recommend changing this to AWS or SMTP as soon as possible, to ensure emails sent from the platform are being sent from an email address within your firm.