Currently maildrop can not be installed in Tumbleweed:

zypper in maildrop
Loading repository data...
Reading installed packages...
Resolving package dependencies...

Problem: 1: nothing provides 'libcourier-unicode.so.7()(64bit)' needed by the
to be installed maildrop-3.1.6-1.3.x86_64
 Solution 1: do not install maildrop-3.1.6-1.3.x86_64
 Solution 2: break maildrop-3.1.6-1.3.x86_64 by ignoring some of its
dependencies

Choose from above solutions by number or cancel [1/2/c/d/?] (c): 

The reason is, that maildrop has a build error since some time.