Many mail programs are able to figure out the settings automatically. If not, consult this page to look for the settings you need
Incoming server: mail.strw.leidenuniv.nl (protocol: IMAP, port 993, connection security: SSL/TLS. Authentication method: Normal password)
Outgoing server: smtp.strw.leidenuniv.nl (port 465, SSL/TLS security. Authentication method: Normal password)
Incoming server: mail.lorentz.leidenuniv.nl (protocol: IMAP, port 993, connection security: TLS)
Outgoing server: mail.lorentz.leidenuniv.nl or smtp.lorentz.leidenuniv.nl (port 25, 465 or 587, STARTTLS security)
Incoming server: mail.physics.leidenuniv.nl (protocol: IMAP, port 993, connection security: TLS)
Outgoing server: mail.physics.leidenuniv.nl (port 25, 465 or 587, STARTTLS security)