Connecting Mailboxes: OAuth vs App Password vs SMTP

Rajat K

New member
May 28, 2025
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When you're setting up email tools or integrating your mailbox into a platform, you’ll often see something like:

Connect via OAuth / App Password / SMTP Credentials.”

Sounds technical, right? It did for me when I first started.

But what do these actually mean, and which one should you use?

Let’s break it down in simple terms.

OAuth: The (Gmail’s Favorite)

Modern email providers love OAuth. Because it's built around security and convenience.

When you use OAuth:

  • You don’t give your password to the app.
  • You’re redirected to your email provider, where you approve access.
  • You can change your main password, and the connected app still works (unless you revoke access).
It’s clean. It’s secure. It’s what Gmail and Microsoft want you to use.

Gmail even made it mandatory. Since May 2022, Google has stopped allowing basic SMTP/IMAP logins unless they go through OAuth.

Example: When you click “Sign in with Google” and approve access, that’s OAuth.

App Passwords: The Next-Best Thing

Sometimes, the app you’re using is a little old-school and doesn’t support OAuth. But your mailbox is secured with 2FA (two-factor authentication).

  • You log into your email provider’s security settings, click “Generate app password,” and you get a one-time password that works just for that app.
  • You don’t share your real password. if this app password is compromised, you can delete it without changing your main one.
Example: You turn on two-factor in Gmail, then create an app password to use in your email client

SMTP Credentials: The Old-School Way

It’s the old-school method where you manually enter your email address, password, and server details (like smtp.example.com). The app uses this info to send emails.

But here’s the problem:

  • You’re giving your actual email password.
  • If the app doesn’t store your password securely, someone could steal it.
  • If your account has 2FA, this method just breaks. your regular password alone isn’t enough to access your account and SMTP doesn’t know how to ask for the second step (2FA authentication code).
Example: Typing your full email and password into a form and entering server info yourself.

Here’s How to Think About It

  • Use OAuth whenever you can. It’s secure and safest.
  • App passwords are a decent fallback, especially with 2FA.
  • SMTP with your main password: Don’t do it. Especially if 2FA is enabled, it’ll fail anyway!
Final Verdict:
Connecting your mailbox isn’t just about “what works.” It’s about what’s safe, future-proof, and respects your data. So choose the safest methods.

Got questions about connecting your mailbox in a cold email platform or a warmup tool? I’m all ears!