The following error occurred while loading notification.so: /usr/lib/claws-mail/plugins/notification.so: undefined symbol: FILE_OP_ERROR I'm assuming this is related to the latest CID fixes.
(In reply to glitsj16 from comment #0) I have just made a git pull, make maintainer-clean, ./autogen.sh, and make Running this build do not show this error and the fix made to the gtk3 branch which run without error is identical to the fix in master (gtk2) which also run here locally. Perhaps running make clean && make will solve your problem?
all works here too.
(In reply to Michael Rasmussen from comment #1) Thanks for your reply. Must have been my mistake, I can confirm this is now working as expected when building from git. Apologies for the noise.