SMTP · App Password

How to connect
Fastmail.

Use a Fastmail app password with mail access and the standard SMTP server.

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 Fastmail plan that includes third-party mail-client access.
  • An app password with mail access; your normal password will not work.

Step-by-step setup

  1. Check your plan and app access

    Fastmail Basic does not include SMTP or app passwords. Confirm your plan supports third-party clients before setting up this connection.

  2. Create an app password for mail

    Open Settings → Privacy & Security → Connected apps & API tokens → Manage app passwords and access. Choose New app password, name it MailboxWarm, and select Mail access before generating the password.

  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
smtp.fastmail.com
Encryption / port
STARTTLS / 587
SMTP username
Your Fastmail login username
SMTP password
Fastmail app password with Mail access

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 password is rejected

Use an app password with Mail access, not the normal account password. Confirm that your plan allows SMTP.

An alias does not authenticate

Use your account’s login username for SMTP authentication. The sending address must be allowed for that account.

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.