TL;DR
If you see a TLS connection error, your server doesn't support TLSv1.2 or higher. lemlist no longer supports TLSv1.0 or TLSv1.1 due to security vulnerabilities. Upgrade your server to TLSv1.2 or higher, or switch to a modern email provider (G Suite, Outlook, Office 365) that supports current TLS versions.
Symptoms
Connection error when trying to connect email account to lemlist
Error message mentions "TLS" or "protocol not supported"
Email fails to authenticate even with correct credentials
Server rejects connection during SMTP/IMAP setup
Environment
Applies to:
Custom email servers running outdated TLS versions (TLSv1.0 or TLSv1.1)
Organizations using legacy on-premises email infrastructure
Email providers that haven't upgraded to modern security protocols
Does NOT apply to:
Gmail, Google Workspace, Outlook, Office 365 (these already support TLSv1.2+)
Step-by-Step Fix
Verify your server's TLS version
Contact your IT department or email hosting provider and ask: "Does our email server support TLSv1.2 or higher?"
✅ Verify: Your IT team confirms TLSv1.2 or TLSv1.3 is enabled on the email server.
Upgrade your email server to TLSv1.2 or higher
If your server only supports TLSv1.0 or TLSv1.1, ask your IT team to enable TLSv1.2. For most modern servers (Exchange, Postfix, etc.), this is a configuration change in server settings.
✅ Verify: Your IT team confirms the upgrade is complete and TLSv1.2 is active.
Test the connection in lemlist
Go to Settings → Sending Settings → Connect new email address. Enter your email credentials and attempt to connect.
✅ Verify: Connection succeeds without TLS-related errors.
Confirm It's Fixed
✓ Email account connects to lemlist successfully
✓ No TLS or protocol-related error messages appear
✓ Test email sends and receives normally through lemlist
Why It Happens / Prevent This
TLSv1.0 (1999) and TLSv1.1 (2006) have known security vulnerabilities, including weak cryptographic algorithms that make them prone to data interception and decryption attacks.
Modern systems (including lemlist, Microsoft, and major email providers) no longer support these outdated protocols to protect user data.
To prevent this:
Use modern email providers (Gmail, Google Workspace, Outlook, Office 365) that automatically support TLSv1.2+
Regularly update your email server infrastructure
Ask your IT team to audit TLS versions annually
Alternatives
Switch to a modern email provider: If upgrading your server isn't feasible, migrate to Google Workspace, Outlook, or Office 365. These providers support TLSv1.2+ by default and require no manual configuration.
Use a different email account temporarily: If you have access to another email address (Gmail, Outlook), connect that to lemlist while your IT team resolves the TLS issue on your primary server.