The following projects are available.
REST based service
Adapt JBMS to send and receive mail using REST. Based on HTTP; an XML/HTTP-ization of POP/SMTP (look at supporting HTTP/SSL). Look at integration with Thunderbird.
IM2000 is a project to design a new Internet mail infrastructure. Puts the storage problem at the sender not the receiver; receivers pick up from the sender. Design and implement IM2001 support for JBMS.
SpecMail2001 is the standard benchmark. Work with the JBMS team to improve its performance. Look at optimizing database access; optimizing Java; optimizing the operating system; etc.