If you're seeing an error while connecting or importing your Maildoso mailboxes into a sequencer like Instantly, Smartlead, Snovio, Email Bison, or PlusVibe, check the error message below for the most likely cause and fix. If your error isn't listed here, also see the broader Can't connect or add mailboxes to your sequencer? and "Error creating sequencer" when connecting Smartlead or Instantly.

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

A 422 usually means the sequencer rejected the mailbox data it received — most commonly because the mailbox's domain isn't fully provisioned yet, or because of a mismatch between the credentials Maildoso sent and what the sequencer expects. Confirm the domain is Active, then retry the import. If it keeps failing for specific mailboxes, contact support with those mailbox addresses. For a deeper walkthrough of this exact error, see Connecting your mailboxes to Instantly.

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 rather than an actual DNS problem. Try re-running 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 are correct on our end.

If a mailbox connects successfully and starts warming up, but then gets silently removed from the sequencer's warmup pool a short time later — with no error shown 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 anything wrong in your setup.

If this is happening to you, contact support with the mailbox address(es), the sequencer you're using, and roughly when the mailbox was dropped from the pool. Re-adding the same mailbox repeatedly without reporting it makes the pattern harder for us to track down, so let us know instead of just re-adding it each time.

If a mailbox connects and sends normally through one tool but the connection fails, drops, or won't verify in a different one — especially right after you enable warmup — this is almost always a stale or mismatched password on the sequencer's side rather than a problem with the mailbox itself. Each tool stores its own copy of the mailbox credentials, so a password change, reset, or reconnect on one tool doesn't automatically update the others.

Fix: open the mailbox's current credentials in your Maildoso dashboard and re-enter them fresh in the tool that's failing, rather than editing the previously saved entry. If it still won't connect after that, contact support with the mailbox address and the name of the tool that's failing.

If the sequencer reports an authentication failure when importing a mailbox, this is usually one of:

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

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) will disconnect any 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 and sequencer.

If mailboxes you connected previously now fail when you try to reconnect or re-import them, while brand-new mailboxes on the same account connect without a problem, this is usually one of two things:

If several previously-connected mailboxes fail this way at once while new ones work fine, contact support with the list of affected mailbox addresses and the sequencer — this pattern usually points to a domain-level DNS issue rather than something wrong with each mailbox individually.

If IMAP connections fail intermittently — timeouts, dropped connections, or auth errors that come and go rather than failing consistently — and it's affecting a cluster of mailboxes rather than just one, this can be a transient issue on a specific piece of our mail server infrastructure rather than anything wrong with the mailbox credentials. Retrying usually works once the underlying instability clears.

Some sequencers fetch a one-time verification code automatically when connecting a Google Workspace mailbox. If this fails with an OTP/code-fetch error, first confirm the mailbox shows Active in your Maildoso dashboard — a Pending or Failed Google Workspace mailbox won't have a working inbox yet to fetch a code from (see Google Workspace mailboxes: availability, provisioning, and "0 available" errors). If the mailbox is Active and the OTP fetch still fails, contact support with the mailbox email and the sequencer you're using.