This is great food for thought and a good opportunity for learning, thank you again.
So generally speaking, we should use yum remove, but in cases where there are dependencies that must not be touched, the rpm nodeps option is the right choice. I never before gave this enough attention.
For the Courier-IMAP package however I saw
# rpm -q --whatrequires psa-courier-unicode
no package requires psa-courier-unicode
which in turn should mean that rpm nodeps cannot cause any damage, because there are no dependencies, correct?