Send Notification on a social event or walk used to open the composer on whichever email type happened to be first in the list, with the sender's own contact address as Send from and one-by-one transactional copies to the selected members. For a site whose committee role addresses are the only verified senders, that meant a social event notification could go out under a member's personal address, rewritten by the mail provider, to every member individually rather than as one campaign.
Each event type now has its own "Send Notification Uses Email Configuration" setting under System Settings → Group, alongside the other per-event-type settings. Send Notification opens the composer on that email type, from its committee role address, to its default mailing list as a single campaign. Existing sites are wired up automatically: the migration picks the site's existing Social Events email type for group events and its Newsletter for walks, so nothing changes for anyone until they choose otherwise. The built-in Walk Change Notification is a workflow type and is deliberately not offered.
Sending is also reachable from the event itself now, not only from the edit form. A social event's Publish menu gains "Email members about this event" for social admins, next to Share on social media. A walk's Share menu gains "Email members about this walk" (a campaign on the walk's email type) and "Email the walk leader" (a plain, unbranded email to the leader) for committee members and walk admins; walk leaders on their own do not see either.
The composer also gains a "Show the subject as a heading at the top of the email" switch under the subject line. For a single walk or event the event card already carries the title, so the heading just repeated it; it starts off when the composer is opened from a walk or event and on for everything else; either way the subject stays in the inbox subject line and the switch only controls the heading in the body. Campaigns now render through the same editable body as the preview, so what you see in the preview is what goes out.