..is there a way to mute a topic via the web interface?Yes. As you, Bruce, are fond of saying, the Help page is your friend. :)
The Groups.io home page provides a place to manage the topics you've muted or followed in all of your group subscriptions. The default home page show a list of all of your group subscriptions.
To get there click on the Groups.io logo in the upper left corner.
In the left column you can select a page showing all of the topics from all of your groups, or just those topics you've Muted, or just those topics you've Followed. To change your options for a specific topic find it in one of those lists and click on it. Then you can use the buttons at the top of the topic display to change its selection options.
- Stop email delivery of messages in an unmuted topic.
- Restore email delivery of messages in a muted topic.
- Begin email delivery of messages in a topic you are not following.
- Stop email delivery of messages in a topic you are following.
Note that follow buttons are shown even when your subscription is set to All Messages and muting buttons are shown even when your subscription is set to Following Only. This is for two reasons: first, this allows you to control where messages are displayed here in the Groups.io home page; and second, you may use these buttons to set options on particular topics before you change your message selection mode.
Messages are the sole opinion of the author, especially the fishy ones.