I'm trying to join the google group 'bup-list' and send an email to
firstname.lastname@example.org and received a confirmation email which prompted me to open a link with a token in the URL which constantly fails due to
An error (#291) occured while communicating with the server.
asking me to enter an email address to subscribe. Entering the same address and pressing the subscribe button results in another confirmation email with a different token being sent which causes the same error. I reproduced this in Firefox 61.0.1 and Chromium 68.0.3440.75 on Ubuntu 18.04. I verified that the URL is copied and pasted correctly.
I'm following different solutions from How can I subscribe to a Google mailing list with a non-Google e-mail address? in order to avoid joining the group with a gmail account (or associating my email address with a google account). I tried adding the email I want to join with as alternative email, but that didn't help.
I cannot search for solutions because typing "Google" into Google can break the internet.