Fastmail MX Records: Complete Setup Guide

Fastmail is a privacy-focused email provider popular with professionals and power users. When using a custom domain with Fastmail, you need MX records to route email through their servers.

This guide covers Fastmail MX setup, including the current recommended configuration and additional DNS records.

Fastmail MX Records

For custom domains on Fastmail:

Add both records for redundancy. The primary server (in1) handles most traffic, with in2 as backup.

About Messagingengine.com

You might wonder about "messagingengine.com"—this is Fastmail's parent company and infrastructure domain. It's the correct hostname for Fastmail MX records, not a third-party service.

Fastmail has used this domain for their mail servers since the company's founding. All Fastmail customers use these same MX records regardless of their plan level.

Adding Fastmail MX Records

Step 1: Set Up Your Domain in Fastmail

Before MX records will work:

1. Log into Fastmail at fastmail.com
2. Go to Settings → Domains
3. Click Add Domain
4. Enter your domain name
5. Fastmail provides DNS records to add

Step 2: Access Your DNS Provider

Log into wherever your domain's DNS is managed (your registrar, Cloudflare, etc.).

Step 3: Remove Old MX Records

If migrating from another email provider, delete existing MX records first. Mixed records cause unreliable delivery.

Step 4: Add Fastmail MX Records

Record 1 (Primary):

• Type: MX
• Host: @ (or blank)
• Value: in1-smtp.messagingengine.com
• Priority: 10

Record 2 (Backup):

• Type: MX
• Host: @
• Value: in2-smtp.messagingengine.com
• Priority: 20

Step 5: Verify in Fastmail

Return to Fastmail settings:

1. Go to Domains
2. Select your domain
3. Click Check DNS or Verify
4. Fastmail confirms when records are detected

Alternative: Fastmail-Managed DNS

Fastmail offers to manage DNS for your domain entirely. If you use this option:

• Fastmail hosts your DNS records
• MX records configure automatically
• You manage all DNS through Fastmail's interface
• Requires changing nameservers to Fastmail's

This simplifies setup but means managing DNS in two places if you have complex hosting needs.

Why Two MX Records?

Fastmail uses two MX servers for reliability:

in1-smtp.messagingengine.com (Priority 10): Primary incoming mail server.

in2-smtp.messagingengine.com (Priority 20): Backup server for failover.

Both servers connect to the same Fastmail infrastructure. The backup ensures email delivery continues during maintenance or server issues.

Additional Fastmail DNS Records

Complete your Fastmail setup with these records:

SPF Record (TXT)

v=spf1 include:spf.messagingengine.com ~all

Add this as a TXT record at your domain root (@).

Check at spfrecordcheck.com.

DKIM Records (CNAME)

Fastmail provides three DKIM records. The format is:

fm1._domainkey → fm1.yourdomain.com.dkim.fmhosted.com
fm2._domainkey → fm2.yourdomain.com.dkim.fmhosted.com
fm3._domainkey → fm3.yourdomain.com.dkim.fmhosted.com

Find your exact values in Fastmail settings under your domain's DNS configuration.

Test at dkimtest.com.

DMARC Record (TXT)

v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com

Add as a TXT record with name _dmarc.

Check at dmarcrecordchecker.com.

SRV Records (Optional)

Fastmail recommends SRV records for automatic client configuration:

_submission._tcp → 0 1 587 smtp.fastmail.com
_imap._tcp → 0 0 0 .
_imaps._tcp → 0 1 993 imap.fastmail.com
_pop3._tcp → 0 0 0 .
_pop3s._tcp → 0 1 995 pop.fastmail.com

These help email clients auto-configure. They're optional but improve user experience.

Common Fastmail MX Issues

Verification Failing

• Wait for DNS propagation (up to 48 hours, usually faster)
• Check both MX records are present
• Verify exact hostnames (no typos)
• Confirm priorities are set correctly

Email Not Arriving

• Verify domain is fully set up in Fastmail
• Check email addresses exist for your domain
• Ensure no old MX records remain
• Test MX records with our lookup tool

"Not Authorized for Domain"

Your domain must be verified in Fastmail before receiving email:

1. Add verification TXT record first
2. Complete domain verification
3. Then configure MX records

DKIM Verification Failed

DKIM records are CNAMEs, not TXT records. Ensure:

• Record type is CNAME
• Three separate records exist (fm1, fm2, fm3)
• Values match what Fastmail provides exactly

Fastmail Features With Custom Domains

Once MX records are configured, you can use:

Aliases: Create multiple addresses at your domain.

Catch-all: Receive email to any address at your domain.

Subdomain addresses: Use user@subdomain.yourdomain.com patterns.

Send-as: Send from any address at your domain.

Configure these in Fastmail settings after MX setup is complete.

Migrating to Fastmail

When moving from another email provider:

Before Migration

1. Sign up for Fastmail (all paid plans support custom domains)
2. Add your domain in Fastmail settings
3. Create user accounts/aliases
4. Lower current MX record TTL 24-48 hours before switch
5. Use Fastmail's import feature to migrate existing email

During Migration

1. Remove old provider's MX records
2. Add both Fastmail MX records
3. Verify in Fastmail settings
4. Test with external email

After Migration

1. Confirm email arrives in Fastmail
2. Complete any remaining email import
3. Keep old system accessible briefly
4. Decommission old provider after 48-72 hours

Fastmail Plans and Limits

All Fastmail paid plans support custom domains:

Basic ($3/month): 1 custom domain, 2GB storage Standard ($5/month): 1 custom domain, 30GB storage Professional ($9/month): 100 custom domains, 100GB storage

MX record setup is identical across all plans. Storage and domain limits differ.

Monitor Your MX Records

Checking once is good. Monitoring continuously is better. The Email Deliverability Suite watches your SPF, DKIM, DMARC, and MX records daily and alerts you when something breaks.