no email comes back from Roundcube Announcement mailing list

[linpi]

I tried to register with announce.lists.roundcube.net, but I never received a confirmation email. I added lists.roundcube.net to the whitelist on the mail server, but nothing has appeared in my log file.
I also checked for any firewall or Fail2Ban blocks, but found none.
Does anyone have any idea what the problem could be?