Seeing "authentication failed", a 535 error, or an IMAP connection failure when connecting a mailbox to your sequencer? Work through these in order:
Use the exact details from a fresh CSV export. On the Email accounts page, re-export the CSV and copy the credentials from there. Your IMAP host is specific to the server your mailbox is on (for example
imap.helicon.maildoso.comorimap.apollo.maildoso.com) — use the host shown in your CSV, don't assume a single host for every mailbox.Check the ports: IMAP 993 with SSL on, SMTP 587 with TLS on. Reconnect the mailbox in your sequencer with those settings.
Brand-new mailboxes that fail even with the correct settings
If the mailbox was created recently and you're using the correct credentials, host and ports but it still returns an IMAP / authentication error, this is a known provisioning issue on our side — not something wrong with your setup. The fix is a quick IMAP-auth correction we run from the backend.
In this case, please don't keep recreating the mailboxes or re-exporting the CSV — it won't resolve it. Just contact support with the affected mailbox names and domains, we'll run the fix, and then you can reconnect (it usually connects right away afterward).
For Google Workspace mailboxes specifically, note they don't use the smtp.maildoso.com host at all — see Logging in to your Google Workspace mailboxes.