claws-mail-pgpcore software package provides virtual package provided by claws-mail-pgpmime, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install claws-mail-pgpcore
claws-mail-pgpcore is installed in your system.
Make ensure the claws-mail-pgpcore package were installed using the commands given below,
$ sudo dpkg-query -l | grep claws-mail-pgpcore*
You will get with claws-mail-pgpcore package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | claws-mail-pgpcore |
| Version | |
| Description | virtual package provided by claws-mail-pgpmime |
| Sub Section | Virtual |