Fastmail + IONOS

Set up Fastmail on IONOS

The records Fastmail needs, written with the field names IONOS uses (Host name, Points to, Value, Alias), in the order to add them.

  • 4 steps
  • 7 DNS records

Before you start

  1. Have your Fastmail account ready. Some values are unique to your account and come from the Fastmail Settings .
  2. Open DNS at IONOS: Sign in at login.ionos.com, select Menu, then Domains and SSL. Under Actions for your domain, select the gear icon, then DNS.
  3. Keep both tabs open and add the records below one at a time.

Records to add

Copy each value with the button next to it. Rows marked “Copy from Fastmail Settings” are unique to your account.

MX records Where incoming email goes Type MX Host name @ Value in1-smtp.messagingengine.com Priority 10 TTL Default
MX records Where incoming email goes Type MX Host name @ Value in2-smtp.messagingengine.com Priority 20 TTL Default
SPF record Which servers may send as you Type TXT Host name Leave empty Value v=spf1 include:spf.messagingengine.com ?all Priority n/a TTL Default
DKIM A signature on every message Type CNAME Host name fm1._domainkey Value fm1.yourdomain.com.dkim.fmhosted.com Priority n/a TTL Default
DKIM A signature on every message Type CNAME Host name fm2._domainkey Value fm2.yourdomain.com.dkim.fmhosted.com Priority n/a TTL Default
DKIM A signature on every message Type CNAME Host name fm3._domainkey Value fm3.yourdomain.com.dkim.fmhosted.com Priority n/a TTL Default
DMARC record What to do with fakes · recommended Type TXT Host name _dmarc Value v=DMARC1; p=none; Priority n/a TTL Default

Step by step in IONOS

Point your MX records

MX records tell other mail servers where to deliver your email. How MX works

Type
MX
Host name
@
Priority
10
Points to
in1-smtp.messagingengine.com
Type
MX
Host name
@
Priority
20
Points to
in2-smtp.messagingengine.com

In IONOS

  1. Select Add record, then the MX section.
  2. Enter @ as Host name, the mail server in Points to, and the Priority. Choose 1 hour for TTL.
  3. Select Save.
  4. If other MX records are listed, delete each one with the Delete record (trash can) icon.
  5. Repeat for each MX record above.

Add the SPF record

SPF lists the services allowed to send email as you. How SPF works

Type
TXT
Host name
Leave this field empty
Value
v=spf1 include:spf.messagingengine.com ?all
  • This is the exact value from Fastmail's manual DNS guide, which ends in ?all (neutral).

In IONOS

  1. Select Add record, then the TXT section.
  2. Leave Host name empty for your bare domain, paste the Value, and choose a TTL.
  3. Select Save.

Set up DKIM

DKIM signs your mail so receivers can trust it. How DKIM works

Type
CNAME
Host name
fm1._domainkey
Alias
fm1.yourdomain.com.dkim.fmhosted.com
Type
CNAME
Host name
fm2._domainkey
Alias
fm2.yourdomain.com.dkim.fmhosted.com
Type
CNAME
Host name
fm3._domainkey
Alias
fm3.yourdomain.com.dkim.fmhosted.com

In IONOS

  1. Select Subdomains, then Add subdomain, and enter the record's name (for example autodiscover).
  2. Under Actions for the new subdomain, select the gear icon, then DNS.
  3. Select Add record, then the CNAME section.
  4. Enter the target in the Alias box, tick the I am aware disclaimer if it appears, and select Save.
  5. Repeat for each CNAME record above.

Add the DMARC record (recommended)

DMARC tells receivers what to do with mail that fakes your domain. How DMARC works

Type
TXT
Host name
_dmarc
Value
v=DMARC1; p=none;

In IONOS

  1. Select Add record, then the TXT section.
  2. Leave Host name empty for your bare domain, paste the Value, and choose a TTL.
  3. Select Save.

Check your setup

Once the records are saved, run a live check. We look up your domain in public DNS and tell you what is right, missing or wrong, with the fix in IONOS’s words.

We only read public DNS records. Nothing is stored.

Common mistakes with Fastmail on IONOS

Adding fewer than three DKIM records

Fastmail signs with three selectors (fm1, fm2, fm3). All three CNAMEs are required.

Adding a second SPF record

Only one record may start with v=spf1. Merge Fastmail's include into the existing one.

IONOS: CNAME records go on their own subdomain

IONOS supports only one top-level CNAME record, so each CNAME is created by first adding a subdomain and then giving it an Alias.

IONOS: MX and a top-level Autodiscover CNAME can't coexist

IONOS doesn't allow a domain to have both an MX record and a top-level Autodiscover CNAME. Microsoft's guide uses the subdomain method above for Autodiscover.

Visit Fastmail Visit IONOS

Fastmail on IONOS: questions

Where do I add Fastmail DNS records in IONOS?

Sign in at login.ionos.com, select Menu, then Domains and SSL. Under Actions for your domain, select the gear icon, then DNS. Add each record there, one at a time.

What goes in the Host name field at IONOS?

Leave it empty for records on your bare domain, such as MX and SPF. For the others, enter only the part before your domain, for example fm1._domainkey. IONOS adds your domain automatically.

Do I need to delete my existing MX records at IONOS?

Yes. Sending servers pick an MX record by its priority (lowest number first) and fall back to the others, so a leftover MX record can receive some or all of your mail. Keep only the Fastmail MX records and delete the rest.

Where do I get my Fastmail DKIM record?

Fastmail DKIM records are CNAME records whose value includes your domain, for example fm1.yourdomain.com.dkim.fmhosted.com. Copy the exact values for your domain from the table on this page.

Sources

Every value and step on this page comes from these official pages. Dashboards change, so if something doesn’t match what you see, tell us.

IONOS steps and tips

Some of these are other email providers' official guides for IONOS. They describe the same IONOS dashboard.

Fastmail on other hosts

Other email providers on IONOS