Warming up
Connect Google Workspace over OAuth, Microsoft 365 over OAuth, or anything else over IMAP and SMTP — then manage fifty of them grouped by domain, with health, quota and authentication visible per row.
Twenty mailboxes looks like diversification until you notice that eighteen of them sit on one domain. If that domain's reputation falls, all eighteen stop delivering at the same moment. Warmerly groups the accounts table by domain and shows an average health per domain, so the concentration is the first thing you see rather than something you discover during an outage.
Mailboxes disconnect for ordinary reasons: a password rotation, an expired token, a host with a bad afternoon. Warmerly retries paused mailboxes on a schedule rather than leaving them dark until someone happens to look, and it distinguishes a genuine authentication rejection from a temporary reachability problem — because treating a wrong password as a transient fault means retrying forever, and treating a transient fault as a wrong password means a mailbox silently stops working.
Each mailbox row carries its health score, today's quota and how much of it is used, and what it has sent and received today. When a row needs attention it says so, and the mailbox page underneath explains why in a sentence rather than an error code — including why today's limit is the number it is.
Sending at any real volume means running more than one mailbox, and running more than one mailbox means the operational problem stops being 'can I connect' and becomes 'which of these fifty is quietly broken'. This is the screen that answers that, and it is built around a single principle: no mailbox should be able to fail silently.
Google Workspace and Microsoft 365 connect over OAuth. You authorise Warmerly in your provider's own consent screen and no password is ever handed over or stored. Tokens refresh in the background, and if consent is revoked the mailbox reports that specifically rather than as a generic failure.
Everything else connects with standard IMAP and SMTP credentials — Zoho, Fastmail, Namecheap, IONOS, Hostinger, a self-run Postfix, and effectively any business mail host. Credentials are encrypted at rest. Warmerly needs both protocols because warmup is a two-sided process: SMTP to send, IMAP to read what arrived, rescue it from junk and reply from the thread.
If IMAP reads fine and sending returns 535 5.7.139, that is not a credential problem. Microsoft now ships tenants with SMTP AUTH disabled by default, and an administrator has to re-enable authenticated SMTP for the mailbox. Warmerly names that case explicitly instead of reporting a generic auth error, because the two need completely different fixes.
The instinct when scaling sending is to add mailboxes. The mistake is adding them all to the same domain. Reputation is scored primarily at the domain level, so twenty-five mailboxes on one domain do not give you twenty-five independent reputations — they give you one reputation with twenty-five ways to damage it, and a single point of failure that takes your entire sending capacity down together.
Warmerly surfaces this in two places. The accounts table groups by domain with an average health per group, so the shape of your setup is visible at a glance. And a campaign's launch-readiness check raises a deliverability-posture warning when too many of its senders share one domain — before the campaign starts, rather than in the post-mortem.
Each mailbox has a daily allowance derived from the real age of the domain and the mailbox, adjusted by that mailbox's live health and measured spam placement. Warmup traffic and campaign traffic both draw from it, which means a campaign cannot push a mailbox past what its reputation currently supports by competing with warmup for the same headroom.
There is also a per-mailbox limit you can set directly, and it is worth knowing that it is a ceiling rather than a target — the derived allowance can be lower, and the lower of the two wins. A mailbox limit set optimistically on a two-week-old domain does not raise anything; it just sits above the number the system will actually use.
Accounts is not only mailboxes. LinkedIn accounts and WhatsApp numbers connect on their own tabs in the same screen, because from a campaign's point of view they are all senders — things a sequence step can be assigned to, each with its own connection state and its own daily action limits.
Keeping them together matters for a practical reason: a multi-channel sequence that references a LinkedIn account which quietly disconnected will stall at that step. One place that shows every sender's state means one place to check before a launch.
Work backwards from volume and from what each mailbox can safely carry. A warmed mailbox on an established domain can sustain a few dozen cold sends a day without stress; a young one carries far less, and forcing it does lasting damage. If you need 500 sends a day, that is a question about how many warmed mailboxes across how many domains, not about finding a mailbox that will send 500.
The other half of the answer is domains. Spreading twenty mailboxes across four domains gives you four reputations and a failure that costs a quarter of your capacity rather than all of it. It costs more and it is more setup — which is exactly why OneMail exists.
Warmerly connects over IMAP and SMTP to send warmup mail, read what arrived, rescue messages from junk, and sync campaign replies into the unified inbox. It is a mail client connection. What it does with that access is documented, and personal mail unrelated to campaigns is not surfaced or analysed.
For Google and Microsoft, OAuth is the supported path and the safer one — nothing to rotate, nothing stored. Other hosts use normal IMAP and SMTP credentials, encrypted at rest.
Usually a rejected authentication or a host that became unreachable. Warmerly distinguishes those two and retries the reachability case automatically. A rejected credential needs you to re-enter it — and on Microsoft 365 it is very often the tenant's SMTP AUTH setting rather than the password.
Plans are sold by mailbox count, and the tiers run from a single mailbox to fifty. Sending volume itself is not metered.
No. Reputation is scored at the domain level, so mailboxes on a single domain share one reputation and fail together. Spread them across several sending domains — Warmerly warns you in the accounts table and again at campaign launch when the concentration is risky.
OAuth for Google and Microsoft, IMAP and SMTP for everything else. Warmup starts the same day, at a volume its age can carry.