For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Thaodan:devel:tools:scm/openSUSE_Tumbleweed/home:Thaodan:devel:tools:scm.repo
zypper refresh
zypper install git-email
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Thaodan:devel:tools:scm/15.5/home:Thaodan:devel:tools:scm.repo
zypper refresh
zypper install git-email
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Thaodan:devel:tools:scm/15.4/home:Thaodan:devel:tools:scm.repo
zypper refresh
zypper install git-email