Ldd

ldd as found on Linux or a BSD displays what dynamic dependencies to a dynamic program exist. Some may even tell of breakage of libraries that don't exist anymore.

[pjp@proteus pjp]$ ldd /usr/bin/fetchmail.old
       libkrb4.so.2 => /usr/kerberos/lib/libkrb4.so.2 (0xb7fd2000)
       libdes425.so.3 => /usr/kerberos/lib/libdes425.so.3 (0xb7fce000)
       libkrb5.so.3 => /usr/kerberos/lib/libkrb5.so.3 (0xb7f70000)
       libcrypt.so.1 => not found
       libdl.so.2 => /lib/libdl.so.2 (0xb7f6d000)
       libresolv.so.2 => /lib/libresolv.so.2 (0xb7f5c000)
       libcom_err.so.3 => /usr/kerberos/lib/libcom_err.so.3 (0xb7f5a000)
       libcrypto.so.4 => /lib/libcrypto.so.4 (0xb7e63000)
       libssl.so.4 => not found
       libhesiod.so.0 => /usr/lib/libhesiod.so.0 (0xb7e5f000)
       libgssapi_krb5.so.2 => /usr/kerberos/lib/libgssapi_krb5.so.2  (0xb7e4c000)
       libc.so.6 => /lib/libc.so.6 (0xb7d24000)
       libk5crypto.so.3 => /usr/kerberos/lib/libk5crypto.so.3 (0xb7d14000)
       /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0xb7fee000)
       libz.so.1 => /usr/lib/libz.so.1 (0xb7d06000)

As you can see libssl and libcrypt aren't there anymore causing fetchmail.old to crash when used.