Quick Note looks like you cant remove dovecot without also removing dovecot-sieve
error: Failed dependencies:
dovecot >= 1.2 is needed by (installed) dovecot-sieve-0.1.19-9.1.el5.x86_64
Also once you removed dovecot-sieve
And you do the install dovecot-2 installs fine but managesieve and pigeonhole have issues.
rpm -ivh dovecot-managesieve-0.4.1-28.el5.x86_64.rpm dovecot-pigeonhole-0.4.1-28.el5.x86_64.rpm
warning: dovecot-managesieve-0.4.1-28.el5.x86_64.rpm: Header V4 DSA signature: NOKEY, key ID 66534c2b
error: Failed dependencies:
dovecot >= 1:2.2 is needed by dovecot-pigeonhole-0.4.1-28.el5.x86_64
This is on Red Hat Enterprise Linux Server release 5.6