Campaign stuck at 'sending' and not progressing

That's a lot slower than expected for that volume. Can you check Settings > Sending to confirm your SMTP connection is showing as “Connected” and not showing any recent error? A stalled campaign like this is usually the sending connection silently failing partway through and the queue backing up behind it.

Hold off on canceling for a moment — I'm pulling up your account's send queue directly to see what's actually happening server-side rather than guessing from the dashboard status. One moment.

Found it — your SMTP provider started rate-limiting our connection partway through (we were seeing repeated 421 “too many connections” responses from their server), which caused the queue to back up waiting on retries. I've adjusted your account's sending throttle to stay under their limit, and the queue is processing normally again now — should finish within the next 20 minutes or so. No need to restart the campaign, it'll pick back up where it left off.