Is an issue with the latest version that hopefully soon will be solved.
In the meantime, you can edit /usr/bin/mailspring and remove _USER_FLAGS from lines 36 and 38 to make Mailspring work.
Source of this is the aur package repo, and it works 
Is an issue with the latest version that hopefully soon will be solved.
In the meantime, you can edit /usr/bin/mailspring and remove _USER_FLAGS from lines 36 and 38 to make Mailspring work.
Source of this is the aur package repo, and it works