Iterable Message Type ID validation now happens when you open settings

If you’ve connected Letterhead to Iterable and configured a Message Type ID for a newsletter, Letterhead now checks whether that ID still exists in your Iterable project every time you open your newsletter settings. If the ID has been removed from Iterable, you’ll see a warning directly under the field — so you can correct it before attempting to preview or send.

Previously, an invalid Message Type ID would fail silently at preview or send time, making it harder to diagnose the issue.

Additionally, if Letterhead cannot reach Iterable at the moment you save your settings (due to a temporary outage or network issue), your settings will save successfully anyway. Only Message Type IDs that Iterable explicitly rejects are refused.