Overview
Keep your mailboxes healthy and connected with clear sending guidelines, smart pacing, and fast restore steps. This help centre article is structured with the reasons for disconnection first, followed by practical fixes and a short recovery checklist.
Sending pattern and pacing
Emails sent less than 10 minutes apart
Total daily volume exceeding safe caps (warmup + outbound combined)
Sudden spikes in volume after a quiet period
Same mailbox used by multiple campaigns without spacing
Using two sender tools at once, for example Smartlead and a competitor
Warmup and migration
Outbound starts before completing an initial warmup period
Switching from another sender or warmup tool without re-ramping
Importing “pre-warmed” mailboxes but not giving them time on Smartlead infrastructure
Reputation and list quality
Bounce rate consistently above 3 to 5 percent
Recipients marking messages as spam
Overused or low-reputation sending domain or tracking domain
Authentication or credential changes
Password or 2FA changed, OAuth token expired or revoked
SMTP or IMAP credentials updated but not refreshed in Smartlead
Provider safety controls
Temporary throttles or policy checks from Microsoft 365 or Google
Suspicious sign-in prompts that require re-consent
Domain configuration
Missing or misaligned SPF, DKIM, DMARC
A. Sending pattern and pacing
Set a minimum time gap of 10 to 15 minutes per mailbox
Keep daily caps within 40 to 50 during early stages and include warmup + outbound
Stagger campaigns so one mailbox does not send from multiple schedules at once
Use one sending platform per mailbox
B. Warmup and migration
Re-ramp on Smartlead with a conservative path for new or cold mailboxes:
Days 1 to 7: 5 to 10 emails per day
Days 7 to 14: 10 to 20 emails per day
Days 14 to 21: 30 to 50 emails per day
Review SmartDelivery results before increasing caps
C. Reputation and list quality
Clean lists regularly, suppress hard bounces and role addresses
Target precisely and keep copy user-friendly to limit complaints
Use a clean sending domain and a branded tracking domain
D. Authentication or credential changes
Reconnect the mailbox and complete OAuth prompts
If using SMTP, update credentials and app-passwords where required
E. Provider safety controls
Reduce pace and total volume, then resume gradually
Align sending windows to recipient business hours
F. Domain configuration
Validate SPF, DKIM, DMARC for the sending domain
Keep the From name and From address consistent across campaigns
Open Mailboxes and confirm the status of the affected mailbox
Reconnect and complete OAuth or refresh SMTP credentials
Lower the daily cap to a safe level that includes warmup + outbound
Set minimum time gap to 10 to 15 minutes
Pause overlapping campaigns sharing the same mailbox
Clean recent bounces or complaint sources, then re-ramp using the schedule above
Run a SmartDelivery test before scaling
Minimum gap: 10 to 15 minutes between consecutive sends
Daily cap during early stages: 40 to 50 total (warmup + outbound)
Warmup path: 5–10 → 10–20 → 30–50 over 21 days
One platform per mailbox; avoid overlapping schedules
Mailbox settings: minimum time gap and daily cap
Campaign schedule: pacing and staggering
SmartDelivery: seed list tests and placement results
Master Inbox: reply monitoring and quick list actions
Outlook tenant error 550 5.7.708 Access denied
https://helpcenter.smartlead.ai/en/articles/81-outlook-tenant-error-550-57708-access-denied
Google error 534 5.7.9 Application specific password required
https://helpcenter.smartlead.ai/en/articles/79-google-error-invalid-login-534-579-application-specific-password-required
Troubleshooting Sending Quota Exceeded
https://helpcenter.smartlead.ai/en/articles/22-troubleshooting-sending-quota-exceeded-error
Data Command Failed 550 5.4.5 Daily user sending quota exceeded
https://helpcenter.smartlead.ai/en/articles/45-data-command-failed-550-545-daily-user-sending-quota-exceeded
Does warmup count toward my daily cap
Yes. Warmup plus outbound equals your total daily sends.
What minimum time gap should I use
Set 10 to 15 minutes per mailbox. Increase the gap as you raise volume.
Can I use another sender alongside Smartlead
Use one platform per mailbox to prevent double scheduling. If another tool is required, dedicate a separate mailbox.
How long should I warm up before scaling
At least 14 days for new or cold mailboxes. Scale gradually based on SmartDelivery results.
Where can I adjust these settings
Mailbox settings control time gap and daily cap. Campaign schedules handle pacing. SmartDelivery and Master Inbox help you verify placement and monitor health.
