Angle quotation marks, colloquially 'angle brackets'.
Breakage at, for example, the seventh of seven links in
– I guess, the ) is misinterpreted.
I have half-learnt to work around comparable breakage in Bugzilla for FreeBSD, however the breakage in e-mail archives is a surprise to me (maybe I never noticed it before).
this is a bug in hypermail, I will fix asap.