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Productivity · head to head

Fastmail vs Syncthing

Fastmail logo

Fastmail

Productivity

Paid email hosting with custom domains, calendar and contacts, run without ad-based revenue

From
$3/month
Rated
-
Full reviewWebsite
Syncthing logo

Syncthing

Utilities

Continuous file synchronisation between your own devices

From
Free
Rated
-
Full reviewWebsite

The short version

  • Only Syncthing has a free tier, so it costs nothing to try first.
  • Each has a real cost: Fastmail it does not provide end-to-end encryption by default, so users specifically wanting zero-knowledge mail should compare it against Proton Mail or Tuta rather than assume parity.; Syncthing synchronisation, not backup: a deletion propagates to every device, and versioning must be configured deliberately
  • They diverge on capability: Fastmail covers Custom domain hosting, Syncthing covers Peer-to-peer sync.
  • Prices and features above were last checked on 1 September 2026.

Where they differ

Only the attributes on which Fastmail and Syncthing actually diverge.

Attributes where Fastmail and Syncthing differ
AttributeFastmailSyncthing
Starting price$3/monthFree
Pricing modelPer user per monthOpen source, no licence fee
Free tierNoYes
PlatformsWeb, iOS, Android, macOS, WindowsWindows, macOS, Linux, Android, Docker
CategoryProductivityUtilities

Identical on both: user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in Fastmail

  • Custom domain hosting
  • Masked email
  • Unlimited aliases
  • Integrated calendar and contacts
  • Migration tools
  • JMAP support

Only in Syncthing

  • Peer-to-peer sync
  • Encrypted transport
  • File versioning
  • Selective sync

What people use each for

The jobs each tool is most often brought in to do.

Fastmail

  • Someone who wants their email address tied to a domain they own rather than a free provider they do notnot Syncthing
  • A small business wanting hosted mail on its own domain without running mail server infrastructurenot Syncthing
  • A person leaving Gmail specifically to stop an ad-funded provider processing their mailnot Syncthing
  • A household migrating several accounts to one paid provider with shared billingnot Syncthing

Syncthing

  • Keeping files in step across personal machines without a cloud accountnot Fastmail
  • Syncing data that must not sit on a third-party server for policy reasonsnot Fastmail
  • Replacing a paid cloud storage subscription for sync-only needsnot Fastmail

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

Fastmail

  • It does not provide end-to-end encryption by default, so users specifically wanting zero-knowledge mail should compare it against Proton Mail or Tuta rather than assume parity.
  • Moving to Fastmail is a real migration with DNS changes for a custom domain, unlike installing a client such as Spark or Bluemail over an existing account.
  • There is no free tier at all, so a user just wanting to try it commits to a paid trial rather than a permanently free option.
  • Storage limits on the entry Basic plan are modest next to the free allowance Gmail gives, and heavy attachment users will need Standard or above.
  • Being based in Australia means it falls under Australian data access law, which some privacy-focused buyers weigh differently from Swiss or German jurisdictions used by Proton Mail and Tuta.

Syncthing

  • Synchronisation, not backup: a deletion propagates to every device, and versioning must be configured deliberately
  • Devices must be online simultaneously to sync, so an always-on machine is effectively required
  • Initial setup involves exchanging device IDs and is less approachable than signing into a cloud service
  • No web access to files, since there is no server holding them

Pricing, plan by plan

Fastmail

$3/month
  • Basic$3/month
    • 6GB storage
    • No custom domain support
    • Core mail, calendar and contacts
  • Standard$5/month
    • 60GB storage
    • Custom domain support
    • Masked email and aliases
  • Professional$9/month
    • 150GB storage
    • Multiple custom domains
    • Priority support

Syncthing

Free
  • SyncthingFree
    • Full functionality
    • No usage limits
    • Community support

Which should you pick?

Choose Fastmail if

  • You need custom domain hosting.
  • You work on Web, iOS, Android, macOS, Windows.
  • You also want masked email.
Fastmail review

Choose Syncthing if

  • You need peer-to-peer sync.
  • You want to start without paying.
  • You work on Windows, macOS, Linux, Android, Docker.
  • You also want encrypted transport.
Syncthing review

Questions people ask

Is Fastmail or Syncthing better?
Neither clearly leads. Fastmail starts at $3/month and Syncthing at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, Fastmail or Syncthing?
Syncthing has a free tier; the other does not. Paid plans start at $3/month for Fastmail and Free for Syncthing.
Does Fastmail or Syncthing run on more platforms?
Fastmail runs on Web, iOS, Android, macOS, Windows. Syncthing runs on Windows, macOS, Linux, Android, Docker.
Can I use Syncthing for free?
Yes. Syncthing has a free tier, so you can try it without paying. Fastmail starts at $3/month.
What is Fastmail best used for?
Fastmail is most often used for someone who wants their email address tied to a domain they own rather than a free provider they do not, a small business wanting hosted mail on its own domain without running mail server infrastructure, a person leaving gmail specifically to stop an ad-funded provider processing their mail, a household migrating several accounts to one paid provider with shared billing. Of those, someone who wants their email address tied to a domain they own rather than a free provider they do not and a small business wanting hosted mail on its own domain without running mail server infrastructure are not what Syncthing is typically brought in for.
What can Fastmail do that Syncthing cannot?
Fastmail covers Custom domain hosting, Masked email, Unlimited aliases, Integrated calendar and contacts. Syncthing covers Peer-to-peer sync, Encrypted transport, File versioning, Selective sync.

Answered from the vendors’ own pages

Fastmail: Is Fastmail a client like Spark, or does it host my email?

It hosts the mailbox itself; there is no separate provider underneath it the way Spark sits over Gmail.

Syncthing: Is Syncthing free?

Yes, open source with no licence fee and no storage costs, because there is no server.

Fastmail: Does Fastmail offer end-to-end encryption?

Not by default in the way Proton Mail or Tuta do; its privacy position rests on being subscription-funded rather than ad-funded.

Syncthing: Is Syncthing a backup tool?

No. It synchronises, so deletions propagate. Use it alongside a real backup, not instead of one.

Fastmail: Can I use my own domain?

Yes, from the Standard plan up, with full alias and masked email support.

Syncthing: Do my files pass through anyone else’s servers?

No. Transfers are peer to peer and encrypted. Discovery and relay servers can help devices find each other, and relayed traffic remains encrypted end to end.

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