See https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=4242 It's marked as resolved, but as I wrote in a commentary there, it was still an issue in 3.17.4-1.1, and it is still an issue in 3.17.4-4.0.
AFAICS the package maintainer is not including¹ the git patches² which fix this issue. Until that happens no update will work for you unless you build yourself from git. If you don't like the build from git way you probably have to wait for a new release or, alternatively, contact and persuade the Arch maintainer include the patches before the release happens ;-) regards, ¹ https://git.archlinux.org/svntogit/packages.git/log/trunk?h=packages/claws-mail&showmsg=1 ² Not sure which one of these is the real fix, for completeness I'd add the three :-) • https://git.claws-mail.org/?p=claws.git;a=commitdiff;h=814f1179a1e5c8f3effd3f4bbfc1c36c16f6a894 • https://git.claws-mail.org/?p=claws.git;a=commitdiff;h=7684d8134420c006cf1de56373009fce9cb857b5 • https://git.claws-mail.org/?p=claws.git;a=commitdiff;h=b6a157f746a0d8a4e23127d7e048f600d1009a01 *** This bug has been marked as a duplicate of bug 4242 ***
Ah, sorry then, thanks for the explanation!