Connected domains are the sending domains behind your connected mailboxes — if your team has connected [email protected] and [email protected], then allegrow.co appears here.
Mailbox reputation problems come in two shapes: a single mailbox misbehaving, or a whole domain sliding — and the fix is very different for each. The Domains endpoints give you the second lens: each domain's reputation is aggregated across all of its connected mailboxes, so a dip here usually means something domain-wide (DNS records, a shared sending pattern, domain-level blocklisting) rather than one person's account.
There's nothing to configure: domains appear automatically as soon as a mailbox on that domain is connected, and carry the same 0–100 reputation scale, tracked daily.
Start with List Connected Domains for the per-domain picture, then Get Connected Domain for one domain's day-by-day history.