You can email your society members via your admin access on the SU website. Unfortunately, we can't share people's email addresses with you just for being members due to GDPR, but you can send a message to every full member from the admin panel.
Please ask your members to make sure that they have opted in for emails for your society/community and for general updates about societies/communities from the SU (under code 7402). If they do not add their email address, they will not receive updates from your society.
They can update their opt in/out options here: https://www.goldsmithssu.org/contactoptions/
See this step by step below, with the History Society as an example, on how to emails to members via the website: