If you can't connect or import your Maildoso mailboxes into a sequencer like Instantly, Smartlead, Snovio, Email Bison or PlusVibe, find your error below for the most likely cause and fix. For step-by-step setup, see How do I upload emails to my cold email tool? and Connecting your mailboxes to Instantly.

In the Export accounts menu on the Email accounts page, the Add all Google accounts to Sequencer / Add selected Google accounts to Sequencer options work for Google Workspace mailboxes only (they use the tools you set up under Settings → Sequencers for GW). If all your mailboxes are SMTP, there's nothing for those options to send — that's expected, not an error.

SMTP mailboxes are imported into the sequencer with a credentials file: go to Email accounts, select the mailboxes, click Export accounts → Download selected accounts as CSV (or Download all accounts as CSV), and use the sequencer's bulk / CSV import. Large batches can be split into several CSVs. Importing by CSV also avoids the verification errors some sequencers hit when they auto-sync a large batch at once. Advanced users can also export credentials through our API with a Personal Access Token and feed them into the sequencer's own API.

You'll see this when you try a one-click sync for SMTP mailboxes. It isn't an error on your account: one-click sync only works for Google Workspace mailboxes, and SMTP mailboxes are not supported for it by design — in every sequencer, with no plans to change. Use the CSV import described above instead.

This appears when linking your sequencer account in Settings → Sequencers for GW. Work through these in order:

If it still fails, it's likely a backend error on our side — contact us with the exact error message and the mailboxes involved.

This generic connection error is usually caused by one of the following:

A 422 means the sequencer (usually Instantly) rejected the mailbox data it received — often an IMAP validation check that failed at the moment of import. Instantly's own support will often point back to Maildoso for this, which is expected. The causes we see, in order of frequency:

A 409 means the mailbox already exists in that sequencer workspace — remove the old or disconnected entry there (not just disconnect it) before importing again.

If the sequencer reports "authentication failed", a 535 error or an IMAP connection failure, work through these in order. (If the connection is refused, hangs or never returns a banner — with no explicit auth error — that's a connectivity issue instead: see IMAP connects but times out, is refused, or returns no response.)

If authentication keeps failing after reconnecting with current credentials, contact support with the mailbox email and sequencer name.

Smartlead is sensitive to brief server-availability blips, and a single failed connection can disconnect your inboxes. Export a fresh CSV (Email accounts → select the affected mailboxes → Export accounts → Download selected accounts as CSV, Smartlead format) and re-upload it in Smartlead — this re-syncs the latest mailbox configuration and resolves most disconnections. An old, previously downloaded CSV usually won't fix it. If mailboxes are disconnected or inactive in your Maildoso dashboard itself, see Why are my mailboxes or domains suddenly disconnected, inactive, or missing?

If mailboxes that were previously connected suddenly show as disconnected with a "Domain unavailable" message, check your domain's status in Maildoso first — a domain that dropped out of Active (for example after a renewal issue or expiry; its mailboxes then show Suspended · Domain expired) disconnects every sequencer relying on it. If the domain shows Active on our side but the sequencer still reports it as unavailable, contact support with the domain name, the mailbox address, the sequencer and roughly when you first saw the error.

Some sequencers run their own MX/SPF/DKIM/DMARC check when you enable warmup, separate from Maildoso's own DNS status. If Maildoso shows your domain as Active and healthy but the sequencer still reports an invalid MX record, this is typically a timing or caching issue on the sequencer's side. Re-run the sequencer's check after a short wait; if it doesn't clear, contact support with the domain name so we can confirm our DNS records on our end.

If a mailbox connects successfully and starts warming up but is silently removed from the sequencer's warmup pool a short time later — with no error and nothing wrong on the Maildoso side — this is a known intermittent issue with warmup delivery pacing that we're actively working on. It isn't caused by your setup.

Contact support with the mailbox address(es), the sequencer and roughly when the mailbox was dropped. Re-adding the same mailbox repeatedly without reporting it makes the pattern harder for us to track down.

If a mailbox works in one tool but fails, drops or won't verify in another — especially right after you enable warmup — it's almost always a stale or mismatched password on that tool's side. Each tool stores its own copy of the credentials, so a password change or reconnect in one tool doesn't update the others. Export a fresh CSV and re-enter the current credentials in the failing tool rather than editing the saved entry. If it still won't connect, contact support with the mailbox address and the tool's name.

If several previously connected mailboxes fail this way at once while new ones work, contact support with the affected addresses and the sequencer — that usually points to a domain-level DNS issue.

If IMAP connections fail intermittently — timeouts, dropped connections, or auth errors that come and go — across a cluster of mailboxes, it can be a transient issue on one of our mail servers rather than the credentials; retrying usually works once it clears. For a single mailbox, treat it as a credentials issue first (see above). If several mailboxes fail the same way at the same time, contact support with a few example addresses and roughly when it started.

Some sequencers fetch a one-time verification code automatically when connecting a Google Workspace mailbox. If this fails, first confirm the mailbox shows Active in your dashboard — a Google Workspace mailbox still in setup or Failed has no working inbox to fetch a code from (see Google Workspace mailboxes). If the sequencer asks you for a verification or reactivation code, it's sent to the individual mailbox — see Verification and reactivation codes from your sequencer.