When a Smartlead mailbox shows as disconnected, read the disconnection reason in Email Accounts first, fix that cause at Google, Microsoft or your SMTP provider, then reconnect and check that the campaign's sender accounts are connected again. The bulk (Re)connect Emails action is a reasonable first try for a batch. A mailbox whose OAuth access was revoked, whose app password changed or whose provider blocked it will drop again unless you fix that first.
Two different problems get called "disconnected": a mailbox that lost its connection to the provider, and a mailbox still in Smartlead but removed from a campaign, which strands that campaign's in-progress leads. The fixes differ, so this guide separates them.
Evidence and disclosure: We checked Smartlead's help center articles on reconnecting accounts, disconnection reasons, re-associating and reallocating leads, campaigns that still don't send and Trigger Logs, plus Google's and Microsoft's token documentation, on October 16, 2026. We did not reconnect a mailbox in a private Smartlead account. Where Smartlead's articles label a button differently, we give both. OutboundXYZ has a Smartlead affiliate relationship; it did not decide these steps.
Which kind of disconnection do you have?
| Where you see it | What it means | First action |
|---|---|---|
| A mailbox in Email Accounts shows an error, or appears under Mailbox Issue Found | Smartlead can't reach the mailbox at the provider | Read the reason (Step 1), fix it (Step 2), reconnect (Step 3) |
| A campaign banner or Attention tab offers Re-Associate Mailbox | The mailbox is still in Smartlead but was removed from this campaign | Re-associate it so stuck leads continue (Step 4) |
| The Attention tab offers Re-Add Account | The mailbox was deleted from your Smartlead account | Re-add it, then re-associate its leads (Step 4) |
| Trigger Logs say "Campaign paused as no eligible email accounts found to send emails." | No active sender is left on the campaign | Reconnect or add an active mailbox, then check the campaign status |
| Trigger Logs say "Credits exhausted or trial expired" | A billing or credit limit, not a mailbox fault | Fix the plan or credits; reconnecting won't help |
Smartlead pauses campaigns for pending payment, exceeded credits, a teammate's pause, or when all of the campaign's mailboxes are disconnected. One disconnected mailbox among several doesn't pause the campaign, but it stops every lead assigned to it.
Step 1: Find the failing mailbox and the exact reason
Smartlead's failed-warmup guide documents where the reason is shown:
- Go to Engage » Sender Accounts to open Email Accounts.
- Open the Mailbox Issue Found tab, or use the filter icon to show Disconnected Mailboxes.
- Select Skip Validation - Show All Issues.
- Click the box with the question-mark icon to see why the account disconnected, then the check solution button for Smartlead's suggested fix.
From a campaign, open Campaign > Performance > Sender Accounts and hover over or click a mailbox's status indicator. Smartlead's SmartAssistant can also run a diagnostic of connection health and OAuth status.
Note the address, provider, connection type (Smartlead's managed OAuth, your own Your Email Network OAuth app, or SMTP), exact error text and affected campaigns. Never paste a password, app password or token into a support chat or screenshot.
Step 2: Fix the cause before you reconnect
Reconnecting only restores the link. Match the error to its cause:
| Error or reason | Likely cause | Fix before reconnecting |
|---|---|---|
OAuth token expired or revoked, or invalid_grant |
Password change, revoked app access, or an admin policy change at Google or Microsoft | Re-run the OAuth flow as the same mailbox and accept every permission screen |
| "This app is blocked" during Google consent | Your Workspace admin hasn't approved Smartlead's OAuth client | Admin approves the client ID; see our Smartlead Google Workspace OAuth guide |
534-5.7.9 Application-specific password required (Gmail via SMTP) |
2-Step Verification is on and the regular password, or a revoked app password, was used | Create a new app password and paste it into the account |
| Outlook sign-in fails after you click Accept | Authenticated SMTP and IMAP are off for the user | Microsoft 365 admin enables both under Users → Active Users → (user) → Mail → Manage Email Apps, then waits 20 to 30 minutes (Smartlead's Outlook guide; full walkthrough in our Smartlead Microsoft 365 guide) |
550 5.7.708 Access denied (Microsoft 365) |
Microsoft blocked outgoing mail from a low-reputation IP, often on trial tenants | An admin requests an exception through Microsoft support; reconnect after the block lifts |
Connection Timed Out (SMTP) |
The SMTP port is blocked | Switch port 465 (SSL) to 587 (TLS/STARTTLS) |
Request failed with status code 504 (Gmail) |
Google flagged or rate-limited the account | Follow Smartlead's 504 steps, including Messages Per Day at 40 or lower |
550 5.4.5 Daily user sending quota exceeded |
Google's sending quota, not a broken connection | Wait for the rolling 24-hour reset and reduce volume |
Why OAuth access "expires." Google's OAuth documentation lists the reasons a refresh token stops working, including revoked access, six months unused, a password change when the token has Gmail scopes (Smartlead's does), and an admin restricting the service (admin_policy_enforced). Google's app-access controls add that when an admin restricts a service, untrusted apps stop working and their tokens are revoked. Microsoft's refresh-token table varies by app type: for confidential clients (apps with a client secret), a user's own password change doesn't revoke the token, but an admin password reset in the Microsoft 365 or Entra admin center does, as does revoking the user's refresh tokens.
If you use Your Email Network (your own OAuth app), check two things Smartlead's guides don't cover. Its Google guide sets the app's audience to External, and Google says External apps left in Testing status get refresh tokens that expire after seven days. If mailboxes drop about a week after connecting, check the project's publishing status. Its Outlook guide recommends a client secret expiry of 90 to 180 days; calendar that date and ask your Smartlead CSM how to rotate the secret, since no rotation procedure is documented.
Step 3: Reconnect the mailbox
Several mailboxes at once
Smartlead's reconnect guide:
- Open the Email Accounts tab and tick the box next to each account. You can select one account, the current page (40), or all accounts from the dropdown.
- Click the Settings icon (gear icon) at the top right of the accounts table.
- In the Advanced Settings panel, click (Re)connect Emails.
Another Smartlead article calls this Bulk (Re)connect email accounts and says it runs in the background and only reconnects the disconnected mailboxes. Our reading, which Smartlead doesn't spell out: a background retry can't collect new OAuth consent or a new app password, so re-authenticate any mailbox that drops again individually.
One OAuth mailbox (Google or Outlook)
Find the mailbox in Email Accounts, choose Reconnect and sign in as the same address, with pop-ups allowed. Smartlead's connection guide says skipped permission screens commonly cause connection errors, so click Allow or Accept on every one. In an agency, the mailbox owner has to sign in. If clients own their mailboxes, agree who handles re-consent in advance; our client access guide covers assigning mailboxes to client logins.
One SMTP mailbox
Open the account's settings, update the password or app password, check the SMTP and IMAP host and port, then save and reconnect. For Gmail, Smartlead recommends moving to OAuth, which avoids the revoked-app-password failure.
Smartlead's public API index lists no reconnect endpoint in the pages we checked. Some third-party connectors reference one, so confirm it with Smartlead before scripting reconnects.
Step 4: Get stranded leads moving again
Smartlead keeps each lead on the same mailbox for the whole sequence so every follow-up stays in one thread. While that mailbox is disconnected, its leads' scheduled emails and replies to those leads won't send. What to do next depends on whether the mailbox is coming back:
| Situation | Action | Tradeoff |
|---|---|---|
| Mailbox reconnected and still on the campaign | Nothing extra; verify (Step 5) | None |
| Mailbox still in Smartlead but removed from the campaign | Re-Associate Mailbox in the Attention tab, or Reassociate under the Action tab in Sender Accounts | None; leads keep their sender |
| Mailbox was deleted, then added back | Re-add it, then re-associate; a re-added account is treated as new | None, once re-associated |
| Mailbox gone for good (suspended account, dropped domain) | Reallocate Mailboxes from the campaign's three-dot menu (live or paused campaigns) | Follow-ups come from a different address |
| No access to the mailbox and no spare senders | Click the Associated Lead/Mailbox count, export those leads, add them to a new campaign | Those leads start a new sequence |
Reallocation needs active mailboxes already on the campaign. If the mailbox will be back within the day, reconnect instead and keep each thread intact.
Then open Edit Campaign (pencil icon) > Final Review > Update Campaign; Smartlead's not-sending guide says changes won't apply without it, even though its newer blog says a campaign resumes on the next sending window unaided. If the campaign shows as paused, resume it once a sender is connected; we found no Smartlead statement on whether an auto-paused campaign restarts itself.
Check warmup too. Smartlead's failed-warmup guide ties a disabled warmup to the disconnection reason, and we found no statement that it turns itself back on, so confirm it's enabled on the mailbox. Smartlead does say email tracking is unaffected once you reconnect.
Step 5: Confirm sending actually resumed
- Email Accounts: the mailbox shows a green Connected status.
- Campaign > Performance > Sender Accounts: no mailbox shows as disconnected.
- Trigger Logs: on the Email Campaign page, click the Trigger Logs icon next to Subsequences and look for "Email sent successfully from {username} to {leadEmail}" from the repaired mailbox. "Mailbox daily send limit reached" points to a different blocker.
- Lead Activity Log: open one lead that was stuck on that mailbox and confirm the next step was sent.
- Master Inbox: replies to that mailbox appear again.
If the mailbox disconnects again within a day or two, the cause from Step 2 wasn't fixed.
If the same mailbox keeps disconnecting
Smartlead's disconnection-reasons article lists sending behavior alongside credential changes: sends less than ten minutes apart, warmup plus outbound volume above safe caps, sudden spikes, two campaigns or sending tools on one mailbox, bounce rates consistently above 3 to 5 percent, spam complaints and missing SPF, DKIM or DMARC. Its checklist suggests a 10 to 15 minute minimum gap and 40 to 50 total daily emails, warmup included, in early stages. That's Smartlead's guidance, not limits we tested.
Check authentication with our SPF record checker and DMARC checker, and see bounce rate reduction if bounces are involved. For SmartSenders mailboxes, Smartlead's Auto-Replace flags "burning" mailboxes and ones near a one-year non-renewal point: a replacement decision, not a reconnect.
Catch the next disconnection sooner
Smartlead's documented webhook events cover sends, replies, bounces, category changes and Campaign Status Changed, but we found no mailbox-disconnected event. Test whether Campaign Status Changed fires when a campaign pauses for lack of senders before relying on it. Our Smartlead and Make guide covers receiving and checking webhook events.
In an August 2024 walkthrough of his agency's automations, Jan described a check against its Smartlead inboxes that ran very early each morning, so the team knew about problems when it started work. A disconnected inbox triggered a Slack message, an automatic reconnection attempt in Smartlead, and a task for a team member to confirm it worked or fix it by hand. The same routine benched weaker inboxes: one whose warmup health score fell below 90% was taken out of outreach rotation for two weeks, then put back automatically. That 90% cut-off was his agency's rule, not a Smartlead threshold, and the video is dated practice, not a test of current Smartlead behavior. The useful split: an automatic retry clears passing errors, and a named person handles the rest.
For the wider platform decision, see our Smartlead review. OutboundXYZ has a Smartlead affiliate relationship; this guide relies on public documentation and one dated Jan video, not a private account test.
Frequently asked questions
Why does my Smartlead account keep disconnecting after I reconnect it?
The cause wasn't fixed. Read the reason under Mailbox Issue Found, then check for a password or 2-Step Verification change, revoked app access, an admin policy change, or the pacing and bounce problems Smartlead lists.
Does one disconnected mailbox stop the whole Smartlead campaign?
No. Leads assigned to that mailbox stop receiving emails until it's reconnected or they're reallocated. Smartlead pauses a campaign when all of its mailboxes are disconnected, or for billing and credit reasons.
Do I need to reassociate leads after reconnecting a mailbox?
Only if the mailbox was removed from the campaign or deleted and re-added. Smartlead says leads must then be reassociated with Reassociate. A mailbox that simply reconnects keeps its leads.
Can I reconnect all Smartlead mailboxes at once?
Yes. Select the accounts in Email Accounts, click the gear icon and choose (Re)connect Emails in Advanced Settings. Mailboxes that need new OAuth consent or a new app password still need individual attention.
