Mailing lists are a natural technology for supporting messaging in multi-party, cross-domain collaborative tasks. However, whenever sensitive information is exchanged on such lists, security becomes crucial. We have earlier developed a prototype secure mailing list solution called SELS (Secure Email List Services) based on proxy encryption techniques [20], which enables the transformation of cipher-text from one key to another without revealing the plain-text. Emails exchanged using SELS are ensured confidentiality, integrity, and authentication. This includes ensuring their confidentiality while in transit at the list server; a functionality that is uniquely supported by SELS through proxy re-encryption. In this work we describe our efforts in studying and enhancing the usability of the software system and our experiences in supporting a production environment that currently is used by more than 50 users in 11 organizations. As evidence of its deployability, SELS is compatible wit...