> Servers and clients are very different in their architecture and implementation
True, but also the only way to really know how to develop a good one is to have experience with building the other.
True, but also the only way to really know how to develop a good one is to have experience with building the other.
I quite disagree here. Servers and clients are very different in their architecture and implementation, and you are going to have very little opportunity for code reuse or even knowledge sharing between the people implementing the client and those implementing the server [1]. I don't think you can turn email servers into a profitable revenue stream unless you do full SaaS, and I don't think Mozilla is really capable of putting in the resources to make a Mozilla Email SaaS feasible.
A better bet would be to try to put together something to more effectively cobble together the existing open-source email server components and do the installation and support as a service, but I again don't think that Mozilla is the organization best-placed to provide that service.
[1] The big exception here is LDAP. But Thunderbird doesn't even really maintain its own LDAP library--it should move to WinLdap/OpenLDAP depending on OS.