to dissect this:
- “authentication failed”: re-enter password in Mail → (sidebar) Settings → Account → Sending mail → Outgoing server (ignoring that /e/ v2.9 bug if the device is on v1.8.1). Also check the email address itself if a typo was introduced
- “retries exceeded”: will inevitably come up after too many auth failures. Though user noted it can come up during smtp being unavailable here and here.