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Custom SMTP guide

Connect your work email when you use Microsoft 365, Google Workspace (SMTP), cPanel, or a company mail server — instead of Sign in with Google.

Before you start

  • You must be logged in to Nexus Mail with an active seat.
  • From address must be the same email as your Nexus login (sender lock).
  • Have your SMTP password ready (often an app password from IT, not your desktop login).

Steps in the app

  1. Open Dashboard → Setup & mailbox.
  2. Choose the Work email (SMTP) tab.
  3. Tap Microsoft 365 or Google Workspace if it matches your provider (you can edit the host).
  4. Enter username and password, then click Test connection & save.
  5. When you see Connected, go to Drafts & send to approve and send.

We test SMTP login before saving. If it fails, check host, port, and password with your IT team.

Typical settings

Provider SMTP host Port Security
Microsoft 365 smtp.office365.com 587 STARTTLS
Google Workspace smtp.gmail.com 587 STARTTLS
cPanel / generic mail.yourdomain.com 587 or 465 STARTTLS or SSL

Username is usually your full email address. Password may need to be an app-specific password if your company uses MFA.

Reply tracking (optional)

Under Advanced: IMAP, you can add IMAP settings so the app can detect replies. If you leave IMAP blank, we try to guess the host from your SMTP server. Use the same password as SMTP unless IT gives you a separate one.

Troubleshooting

Problem What to try
Login failed Confirm port 587 + STARTTLS or 465 + SSL; verify password with webmail.
Wrong email From address must match your Nexus account email exactly.
Google Workspace If OAuth is blocked, use SMTP with an app password.
Microsoft 365 Ensure SMTP AUTH is enabled for your mailbox (ask IT).

Security

  • Passwords are encrypted on the server; we do not show them again after save.
  • Prefer STARTTLS or SSL — avoid plain SMTP unless IT requires it on a private network.

For administrators

  • MAIL_SAAS_ALLOW_SMTP=1 (default) shows the SMTP UI. Set to 0 for Gmail OAuth only.
  • API: POST /api/mailbox/connect/smtp with form fields email, smtp_host, smtp_port, smtp_security, smtp_username, smtp_password, and optional IMAP fields.
  • Rotating MAIL_SAAS_SECRET_KEY requires a migration plan — stored credentials become unreadable.