ports/mail/balsa2 fails to compile with a missing -lgdbm error. The fix was for me to install gdbm manually from ports.
Add a LIB_DEPENDS entry into the Makefile for ports/mail/balsa2 containing the proper dependency for ports/databases/gdbm
LIB_DEPENDS= [...] \
How-To-Repeat: Make sure the databases/gdbm port is not installed.
cd /usr/ports/mail/balsa2 && make
(error manifests itself here)
Over to maintainers.