The Mailboxes tab shows why a mailbox paused. Match the reason to the fix:

When a provider rejects or defers a send, it returns an enhanced status code. The Mailboxes tab and the health strip translate the code into plain language and a fix. Codes that start with 4 are temporary and usually clear on their own; codes that start with 5 are permanent and need a fix before sends succeed.

A list can hold fewer leads than your file had rows, and a sequence can enroll fewer leads than the list holds. They are two different things. The import result on the list page names every row your file lost and why. The attach summary in the builder reads “Ready to enroll: 1 of 5” and lists one line for every reason underneath, so the four that are missing are named rather than counted. Neither of those is a send count: the tiles on Analytics follow the Sequence picker in the page header, which opens on the most recently updated campaign that has sent inside the range you are reading, falls back to All sequences when nothing has sent in that range, and names the scope in force in the caption underneath.

No lead is ever skipped for having been contacted recently. There is no such rule. A lead that stayed in an older list is a lead still active in another campaign, and the review panel says so: the line reads Active in another campaign, and it names that campaign and the step the lead is on underneath whenever it can resolve them. Whether those leads are held back at all is a setting on the campaign, so you can add them anyway on a campaign where that is what you want. Back on the list itself, a lead the last launch passed over carries the reason on its own row, in the Sequence column. What every other skip reason means is in Leads & Import. For a launched sequence, the address-by-address view of who was enrolled and who was passed over is the Recipients drawer in Analytics.

After an import, Laureo reports how many rows were imported and how many were skipped, with reasons: duplicate addresses, matches to existing customers, suppressed addresses, do-not-contact entries, or malformed rows. These skips are protections, not errors. Every skipped row is listed with its address under the reason that caught it, so you can act on the file rather than guess. Review the reasons, fix any genuinely bad rows in your file, and re-import. If the whole import was rejected, the most common cause is a missing list-source attestation.

Cold sends are counted against an enforced monthly ceiling, and that ceiling is per user: on Ultra it is 7,500 cold emails per month per user, so the figure on your meter is your own allowance and every teammate has their own. This is a hard ceiling. Unlike the warn-only campaigns meter, the cold-send meter stops new cold sends once you reach it. When it is exhausted, in-flight sequences defer their remaining sends to the next monthly reset, you get a single notification, and a launch attempt is blocked on the meter gate.

Cold Outreach posts to your normal notifications. A mailbox auto-pause, an exhausted meter, or a sequence blocked at launch all surface in the notifications inbox (and to org admins for mailbox-health events). Keep an eye on the bell so a paused mailbox does not quietly stall a sequence. See Notifications Inbox.