1Check your plan includes SMTP
Fastmail’s Basic plans don’t include IMAP or SMTP access, so they can’t be used here. Standard, Professional and the other non-Basic plans can.
2Create an app password
Fastmail never accepts your regular password over SMTP, with or without two-step verification.
- In Fastmail, go to Settings → Privacy & Security.
- Under Connected apps & API tokens, click Manage app passwords and access.
- Click New app password and confirm your password if asked.
- Name it “FormSMTP” and leave access on Mail, Contacts & Calendars, which covers SMTP.
- Click Generate password and copy it.
3Create the FormSMTP project
Sign up free and add a project. There’s no Fastmail preset in the provider list, so leave it on Custom and type the host and port below.
4Enter the settings
| Provider | Custom |
| Host | smtp.fastmail.com |
| Port | 465 with SSL on. 587 with SSL off (STARTTLS) also works. |
| Username | Your Fastmail address, including the domain |
| Password | The app password from step 2 |
| From email | An address on your Fastmail account, such as your own domain |
Click Test connection, then add your form. See the HTML contact form guide, or compare every provider on the SMTP settings page.
How form emails arrive
FormSMTP signs in to Fastmail as you and sends the submission from your address, with the visitor’s email as Reply-To. The message is a normal email from your own account, so replying from Fastmail goes straight to the visitor, and your Fastmail rules and folders work on it like any other mail. A subject such as “New message from the contact form” (set with _subject) makes a filter easy.
Keep the website’s app password separate
Create one app password just for FormSMTP rather than reusing the one in your phone or desktop app. If you ever stop using the form, or think the password has leaked, delete it on the same Manage app passwords and access screen. Nothing else that signs in to your account is affected.
Sending limits
Fastmail sets daily limits per user, by plan, and counts each recipient as one message:
| Plan | Messages a day |
|---|---|
| Standard, Individual, Duo, Family, Business Standard | 8,000 |
| Professional, Business Professional | 16,000 |
| Trial accounts | 120, until the account is paid for |
There’s also an hourly limit of half the daily one, and a 10-minute limit of half the hourly one, plus smaller limits on distinct recipients. A contact form stays far below all of them. Fastmail says its limits are generous for people but not designed for bulk sending, so use a sending service for newsletters.
Common errors
- Authentication failed: you used your Fastmail password instead of an app password, the username is missing the domain, or the account is on a Basic plan.
- Sending stops after 120 messages: the account is still on a trial. The limit lifts once you pay.
- Rate limit errors in a burst: the 10-minute limit is half the hourly one. Spread out large sends, or move them to a sending service.
- Timeouts on 465: use 587 with SSL off; Fastmail supports STARTTLS there.
For anything not listed here, look the code up in SMTP error codes explained.
Sources: Server names and ports · App passwords · Account limits · Trial accounts. Checked November 2, 2026.
FAQ
Can I use my Fastmail password for SMTP?
No. Fastmail only accepts app passwords for SMTP and other mail apps. Create one under Settings, Privacy & Security.
Does Fastmail Basic include SMTP?
No. Basic plans don’t include IMAP or SMTP access. You need Standard, Professional or another plan that does.
Should I use port 465 or 587?
Fastmail lists 465 with SSL/TLS. If your setup only supports STARTTLS, use 587 with SSL off in FormSMTP.
Is Fastmail OK for a website contact form?
Yes. A form sends one email per submission, far below Fastmail’s daily limits. For newsletters or other bulk email, Fastmail recommends a dedicated service.
Why do my messages land in spam?
Usually the From address isn’t on a domain you’ve verified with the provider, or the domain has no SPF and DKIM records. Verify the domain, send from an address on it, and check the Deliverability panel in FormSMTP’s Settings.