[Dovecot] Upgrading from 1.2 to 2.0

Greetings Dovecot mailing list!

We are an ISP that recently migrated from Courier to Dovecot, and are looking at the next round of upgrades. Hoping that we could get pointed to some documentation or get a general list of best practices for an upgrade from 1.2.13 to 2.0.9. Our current environment consists of four Dovecot machines that share an NFS backend hosting POP and IMAP. Our biggest question is whether we can support a rolling upgrade from 1.2.13 to 2.0.9, or if it would need to be an all for one cut.

Thanks in advance.