TL;DR

Most connection issues: Go to Settings → Sending Settings, click trash icon to unlink email, then reconnect with correct SMTP/IMAP settings (verify host, port, SSL enabled, correct credentials). For 'Invalid Grant' errors: Unlink email in Settings → Sending Settings, then reactivate. For timeout errors: Verify no IP restrictions, check the host/port with SSL enabled, and confirm no provider outages.

For issues related to email aliases, note that aliases cannot be connected as separate senders and must use the primary email account instead.

Symptoms

The email account shows Disconnected or Error status in Settings
Error message: "Invalid Grant" when connecting to Gmail/Google Workspace
Connection timeout when trying to connect to email
Campaigns paused with message about email connection issues
Cannot send test emails from connected account
Connectivity issues when attempting to connect an email alias instead of a primary account
Connection status stuck as "Pending" due to Microsoft admin approval requirements

Environment

Applies to all email providers connected to lemlist via SMTP/IMAP or OAuth (Gmail/Google Workspace).

This includes limitations such as the inability to connect email aliases as senders and potential approval requirements for Microsoft organizational accounts.

Note: Some SMTP providers are not supported: SendGrid, Mailgun, Sendinblue, Mailjet, O2switch, Amazon SES, Postmark, Cloudmark, HostGator, and others. Check provider compatibility in Lemlist before connecting.

Step-by-Step Fix

1. Verify SMTP/IMAP configuration

Check these settings match your email provider:

SMTP settings:

Host and port correct for your provider
SSL/TLS enabled
Username (email address) correct
Password correct

IMAP settings:

Host and port correct for your provider
SSL enabled
Same credentials as SMTP

Common ports:

SMTP: 465 (SSL) or 587 (TLS)
IMAP: 993 (SSL)

✅ Verify: Settings match provider documentation exactly

2. Reconnect email account

Go to Settings → Sending Settings

Click the trash icon next to the problematic email

⚠️ Note: This pauses campaigns temporarily

Click Add email and reconnect with updated settings

Test the connection after reconnecting

✅ Verify: Email shows Connected status

3. Check email permissions

Verify your email provider allows third-party app access:

Gmail/Google Workspace:

Check Google Account security settings
Ensure "Less secure app access" is enabled (if applicable)
Verify OAuth permissions granted

Other providers:

Check provider security settings
Enable IMAP access if disabled
Generate an app-specific password if using 2FA
Verify SMTP authentication is enabled in your provider's settings

✅ Verify: Provider allows external app connections

4. Rule out connectivity blocks

Check:

Firewall not blocking SMTP/IMAP ports
No IP restrictions from the email provider
Browser cache cleared
Using the latest browser version

✅ Verify: No network or firewall blocks

Fix Specific Errors

535 Authentication Failed Error

Cause: Issues with authentication or configuration between your email provider's SMTP server and lemlist.

Fix:

Double-check your username and password for typos.
Generate and use an app-specific password if 2FA is enabled.
Verify that SMTP authentication is enabled in your email account settings.
Reconfigure SMTP server and port settings to match your provider's documentation (e.g., SSL enabled).
Unlink your email account from lemlist and reconnect it with updated settings.

✅ Verify: Connection is successful, and test emails send without errors.

Alias Connection Errors

Cause: Attempting to connect an alias instead of the primary account. Fix:

Identify the primary email associated with the alias.
Connect the primary email instead of the alias in Lemlist.
Warm up the primary account for optimal email deliverability (impacts the alias as well).

Pending Microsoft Account Approval

Cause: Organizational restrictions requiring admin consent for third-party app access. Fix:

Contact your Microsoft account administrator.
Request approval for Lemlist in the Microsoft Entra Admin Center.
Retry connecting your account after admin approval.

Account Overlap Issues

Cause: The email is already linked to another Lemlist account. Fix:

Locate the Lemlist account currently linked to the email.
Disconnect the email from the original account.
Connect the email to the intended account.

Invalid Grant Error (Gmail/Google Workspace)

Cause: Expired OAuth token or revoked permissions

Fix:

Go to Settings → Sending Settings
Click the trash icon to deactivate the email
Click Add email to reactivate
Re-authorize when prompted

✅ Verify: Can send test email without errors

Connection Timeout

Cause: IP restrictions, incorrect settings, or provider outage

Fix:

Verify the host and port are correct with SSL enabled
Check no IP restrictions blocking lemlist servers
Contact the provider to confirm no outages
Try a different network if on a restricted corporate network

✅ Verify: Connection completes without timeout

Provider-Specific Settings

Zoho Mail

Enable IMAP: Settings → Email Accounts → Configure IMAP
Use these settings:
- IMAP: imappro.zoho.com (Port 993)
- SMTP: smtp.zoho.com (Port 465)
Generate app-specific password if using 2FA

Lark

Manually type settings (don't copy-paste)
Enable SSL encryption
Verify all required fields filled
Confirm credentials valid in Lark settings

OVH Mail Pro

Ensure SMTP server address and port are configured properly:
- SMTP Server: pro?.mail.ovh.net (replace '?' with appropriate server number), Port: 587, SSL disabled.
- IMAP Server: pro?.mail.ovh.net, Port: 993, SSL enabled.
Verify credentials and enable SSL encryption.
Confirm all required fields are filled in the configuration.

Confirm It's Fixed

✓ Email account shows Connected status in Settings

✓ Test email sends successfully

✓ Paused campaigns resume automatically

✓ No error messages in Sending Settings

Why It Happens

Connection issues occur when SMTP/IMAP settings are incorrect, OAuth tokens expire, email providers block third-party access, or network firewalls block connections. Providers may also have temporary outages or security restrictions.

Prevent this: Use correct provider settings, keep OAuth permissions current, enable IMAP access, and generate app-specific passwords for 2FA accounts.