The email addresses that MemberMouse makes available are those of the Employee Accounts you have setup in General Settings > Employees. In some cases you can choose which email address is used, in others the default account is used. The default employee account is marked with the ‘orange flag' icon.
The Welcome Email's ‘From:' address can be changed by editing the membership level in Product Settings > Membership Levels > Edit (pencil icon) > Welcome Email > and selecting the desired address in the ‘From' dropdown box.
The Push Notification's ‘From:' address can be changed from Developer Tools > Push Notifications > Edit > and selecting the address in the ‘From' dropdown box.
Reset Password emails will be sent from the default employee email (as indicated by the orange flag) in General Settings > Employees.