SMTP · domain credentials

How to connect
Mailgun.

Choose the SMTP credentials and regional endpoint for your Mailgun sending domain.

Connection preview. You can read this guide and save a mailbox for later. Live authorization and warm-up remain off. Do not enter real credentials while the connection form is disabled.

Before you start

  • A configured Mailgun sending domain and authorized sender address.
  • The SMTP credentials for that domain, not an HTTP API key.

Step-by-step setup

  1. Open your domain’s SMTP credentials

    In Mailgun, go to Sending → Domain Settings, select the sending domain, and open SMTP Credentials. Use the SMTP username and password for that domain.

  2. Match the server to your region

    Use the US or EU outgoing SMTP endpoint that matches the domain. A domain’s SMTP credentials and region must agree.

  3. Choose Other provider in MailboxWarm

    Open Mailboxes → Add mailbox, choose Other provider, and enter your sending email address. Named SMTP services all use this same Other provider connection option.

  4. Enter the connection details

    When connections are enabled, enter the SMTP values listed below. Choose Test & connect. MailboxWarm checks authentication and the encrypted connection without sending a message.

Connection settings

Match these values to the fields in MailboxWarm. Keep passwords and keys private.

Connection option
Other provider
SMTP host · US
smtp.mailgun.org
SMTP host · EU
smtp.eu.mailgun.org
Encryption / port
STARTTLS / 587
SMTP username
Your domain’s SMTP username
SMTP password
Your domain’s SMTP password

SMTP sends; it does not read your inbox. This connection does not include IMAP access to your mailbox. Placement and rescue activity concern the controlled seed inboxes receiving warm-up messages. Provider-specific compatibility still needs live validation.

Check the result

In today’s preview, expect Mailbox saved for later. When connections are enabled, a successful check shows Mailbox connected, with warming still paused. A failed connection check is not proof of delivery or a reason to add the same mailbox again.

Once live warming is available, choose the mailbox’s plan and schedule before starting. Connecting alone does not begin warm-up, and your provider’s sending limits still apply.

Open setup preview

Troubleshooting

The credentials do not work

Check the domain and region, and use SMTP credentials rather than an API key.

The account is restricted

Review your Mailgun domain verification and account restrictions. A successful SMTP login does not remove sending restrictions.

Provider resources

Provider menus and account policies can change. Use their official documentation for the latest requirements.

Settings reviewed September 12, 2026 · Documentation review, not a live connection test.