I upgraded from claws-mail 3.13.2 on Ubuntu 16.04 to claws-mail 3.17.1 on Ubuntu 18.10 and copied my files over. Claws-mail segfaults on start-up, but if I delete my .claws-mail directory, it works fine. I also tried claws-mail 3.16 on Ubuntu 18.04, and it also segfaults on startup when my old IMAP profile is present. This appears to be similar to https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=3855, which was claimed to be resolved. However, the proposed temporary fix of changing 'protocol=3' to 'protocol=1' in accountrc and adding 'config_version=2' to clawsrc does not fix the problem for me.