If your clients or team members are not receiving invitations, password resets, or notifications, the issue is usually related to SMTP configuration. This guide helps EFILERs troubleshoot authentication errors across Gmail, Zoho, SendGrid, AWS SES, Mailgun, Google Workspace, and Custom SMTP providers.
Common errors include:
535 Authentication Failed
535 5.7.8 Username and Password not accepted
Invalid login or SMTP authentication error
Invites not sending or not delivered
Why SMTP Errors Happen
Most email providers no longer allow standard email passwords for SMTP connections. Instead, they require secure credentials such as API keys, app passwords, or provider generated SMTP usernames.
Typical causes:
Using your regular email login instead of SMTP credentials
App password or API key missing
Incorrect SMTP host, port, or encryption method
Two factor authentication enabled without updated SMTP credentials
Provider security blocking external apps
General SMTP Settings Checklist
Before troubleshooting by provider, confirm these basics:
SMTP server is correct
Port is correct (usually 587 TLS or 465 SSL)
Username matches your email or SMTP login
Password is an App Password or API Key if required
TLS or SSL is enabled based on provider instructions
Gmail or Google Workspace Setup
If you see Username and Password not accepted, Google is likely blocking the login.
What to do:
Enable 2 Step Verification on your Google account
Create a Google App Password
Use the App Password in your SMTP settings instead of your regular Gmail password
Standard Gmail SMTP details:
Server: smtp.gmail.com
Port: 587
Encryption: TLS
Zoho Mail Setup
Zoho often returns 535 Authentication Failed when regular login details are used.
Steps:
Confirm SMTP access is enabled in Zoho Mail
Use Zoho provided SMTP credentials
Verify server and port settings
Typical Zoho SMTP:
Server: smtp.zoho.com
Port: 587
Encryption: TLS
SendGrid, Mailgun, AWS SES, and Other Email Services
Third party email services usually require API based SMTP credentials instead of your email login.
SendGrid
Username is often "apikey"
Password is your SendGrid API Key
Mailgun
Username is provided in your Mailgun SMTP dashboard
Password is the Mailgun SMTP password
AWS SES
Use AWS generated SMTP credentials
Do not use your AWS account login
Important:
Always copy SMTP credentials directly from the provider dashboard. Using your normal email password will fail authentication.
Custom SMTP Setup
If you selected Custom SMTP:
Verify the SMTP host matches your provider exactly
Confirm port and encryption type
Use provider generated credentials if available
Avoid extra spaces when pasting passwords or API keys
How to Test If SMTP Is Working
After updating settings:
Save your SMTP configuration
Create a test client or resend an invite
Check inbox, spam, and junk folders
Confirm no new authentication errors appear
If the invite arrives, your SMTP setup is correct.