Why am I getting 554 5.1.8 error code?
Two-Factor Authentication (TFA) adds an extra layer of security to your Zoho account. With TFA enabled, logging in requires both your regular password and a one-time code — typically sent to your registered mobile number.
When TFA is enabled, third-party applications or external email clients (e.g. IMAP/POP clients, CRM platforms, mobile mail apps) cannot use your regular password for authentication. Instead, they require a unique, app-specific password.
When Do You Need an App-Specific Password?
Use an app-specific password if:
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You have enabled TFA for your Zoho account
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You’re setting up Zoho Mail in a third-party app or client (e.g. desktop/mobile email client, CRM tool) that doesn’t support Zoho’s native authentication flow
How to Generate an App-Specific Password — Step by Step
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Log in to your Zoho account
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Navigate to Security → App Passwords in your account settings
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Click Generate New Password
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In the dialog/pop-up, enter a name for the app (e.g. “Outlook,” “Mobile Mail,” “CRM Tool”). — the name is for your reference only.
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Click Generate. A 12- or 16-digit “application-specific password” will be created.
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Copy the password immediately and save it securely — it won’t be shown again.
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Use this app-specific password (instead of your regular Zoho password) when configuring your third-party application or email client.
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Go back to your Investor Matching Email account setup page:
https://www.startups.com/investors/matching - Paste the generated password in both the SMTP Password and IMAP Password fields.
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Click Test Account to verify that the connection is working successfully.
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Once it shows Connected, your email account will be connected and ready to use.
554 5.1.8 Sender Address Blocked
This error indicates that Zoho has restricted your email address from sending outgoing messages due to policy or security concerns.
To resolve this, you must contact Zoho Support so they can review the restriction and unblock your sender address.