IMAP and SMTP will get your mail in and out of almost any client. They will not, on their own, keep your calendar and address book in sync. For that you need a calendar and contacts protocol: Exchange ActiveSync, CalDAV, CardDAV, or a vendor-specific alternative such as Microsoft Exchange or Google’s own apps. This article compares which major business email hosts officially offer ActiveSync, CalDAV and CardDAV, based on current provider documentation checked on November 14, 2026.
Quick answer
Hosts that officially offer all three protocols — with plan limits — include Thexyz Email (paid Sync Upgrade), Zoho Mail (ActiveSync on business-paid plans only), mailbox.org, Kolab Now (ActiveSync on the full Groupware subscription), IONOS Mail Business, and many Zimbra-based hosts (ActiveSync often depends on the commercial edition).
Microsoft 365, GoDaddy Microsoft 365 and typical hosted Exchange providers such as Intermedia support ActiveSync but not native CalDAV or CardDAV. Google Workspace still supports CalDAV and CardDAV (OAuth required); its ActiveSync service, Google Sync, was retired in 2025. Fastmail and Posteo document CalDAV and CardDAV, not ActiveSync. Rackspace Email Plus documents Mobile Sync (ActiveSync), not CalDAV or CardDAV. Proton Mail does not offer any of the three; Proton Mail Bridge is IMAP and SMTP only, on paid desktop plans.
Comparison table
“Yes” means the provider documents the protocol. Plan limits and caveats are in the Notes column and the sections below. This is not a price comparison, and it is not a complete list of every host.
| Provider | ActiveSync | CalDAV | CardDAV | Notes |
|---|---|---|---|---|
| Thexyz Email | Paid add-on | Paid add-on | Paid add-on | All three are part of the Sync Upgrade. IMAP/SMTP mail works without it. Thexyz Classic Email documents ActiveSync (Mobile Sync) only. |
| Zoho Mail | Business-paid only | Yes | Yes | ActiveSync is not available on personal accounts and must be enabled by an admin. Not supported in Outlook for Mac or Apple Mail on macOS. |
| mailbox.org | Yes | Yes | Yes | Mobile sync is listed on Light, Standard and Premium. mailbox.org recommends CalDAV/CardDAV over ActiveSync. App passwords if 2FA is on. |
| Kolab Now | Groupware plan | Yes | Yes | ActiveSync requires the full Groupware subscription and cannot be used at the same time as 2FA. |
| IONOS Mail Business | Yes | Yes | Yes | Official setup guides are for Mail Business mailboxes. Equivalent guides were not found for Mail Basic. |
| Zimbra-based hosts | Varies | Yes | Yes | The Zimbra platform documents all three. ActiveSync (Zimbra Mobile) is typically a commercial / Network Edition feature, so it depends on the host. |
| Microsoft 365 / Exchange Online | Yes | No (native) | No (native) | ActiveSync is on by default for Exchange mailboxes. Official calendar and contact APIs use Microsoft Graph, not CalDAV or CardDAV. |
| GoDaddy Microsoft 365 | Yes | No (native) | No (native) | This is Microsoft 365 email resold by GoDaddy. Set up the account as Exchange on phones. |
| Intermedia (hosted Exchange) | Yes | Not documented | Not documented | ActiveSync can be enabled per mailbox in HostPilot. No official CalDAV or CardDAV setup articles were found. |
| Google Workspace | Retired | Yes (OAuth) | Yes (OAuth) | Google Sync (ActiveSync 12.1) ended for Workspace accounts on May 1, 2025. CalDAV and CardDAV require OAuth 2.0 over HTTPS, not a regular password. |
| Fastmail | Not listed | Yes | Yes | Official server docs cover IMAP, SMTP, CalDAV, CardDAV, JMAP and WebDAV. Basic plans do not include CalDAV or CardDAV. App passwords required. |
| Posteo | Not listed | Yes | Yes | Feature list and help cover CalDAV, CardDAV, IMAP and SMTP. ActiveSync is not mentioned in those official pages. |
| Rackspace Email Plus | Email Plus only | Not documented | Not documented | Mobile Sync (email, calendar and contacts) is limited to Email Plus. Standard Rackspace Email uses IMAP/SMTP on mobile. |
| Proton Mail | No | No | No | Proton Mail Bridge provides local IMAP and SMTP on paid desktop plans only. It is not an ActiveSync, CalDAV or CardDAV server. Calendar and contacts stay in Proton’s own apps. |
| iCloud+ custom domain | No | Native on Apple | Native on Apple | iCloud Mail, Calendar and Contacts sync on Apple devices signed into the same Apple Account. Apple does not offer ActiveSync for iCloud Mail. Current Apple Support pages do not publish CalDAV or CardDAV hostnames for third-party clients. |
What these protocols are, and why they matter
Exchange ActiveSync
Exchange ActiveSync (EAS) is a Microsoft protocol that syncs mail, calendar, contacts and, on many servers, tasks over HTTPS. Phones usually add it as a Microsoft Exchange account. Microsoft documents it for Exchange Online: it is enabled by default, supports Direct Push, and can be turned off or limited with device policies, including remote wipe.
The practical appeal is one account that covers mail, calendar and contacts in the built-in iPhone Mail/Calendar/Contacts apps, many Android “Exchange” account types, and some versions of Outlook. The trade-off is that it is a licensed, vendor-controlled protocol. Open-source and Linux clients often support CalDAV and CardDAV better than ActiveSync. Apple Mail on the Mac and Outlook for Mac typically speak Exchange Web Services or Microsoft’s newer APIs, not ActiveSync, which is why some hosts (Zoho is explicit about this) say ActiveSync will not work there.
CalDAV
CalDAV is an open standard (an extension of WebDAV) for calendar data: events, often reminders or tasks, and calendar sharing. Apple Calendar on iPhone and Mac can add a CalDAV account natively. Thunderbird’s calendar, eM Client, Evolution and many Linux apps speak it too. On Android you usually add a helper such as DAVxâµ rather than a built-in Exchange-style account.
Outlook for Windows does not include CalDAV. The usual workaround is a third-party plugin such as Outlook CalDAV Synchronizer. Microsoft 365 and Exchange Online do not document a native CalDAV endpoint; Microsoft points developers at Microsoft Graph instead.
CardDAV
CardDAV is the matching open standard for address books (vCard data). Apple Contacts supports it natively. Thunderbird and many desktop clients do as well. Android again usually needs a sync app. Same Outlook limitation as CalDAV: no native CardDAV in Outlook, and no native CardDAV documented for Exchange Online.
If you only set up IMAP and SMTP, your phone or Thunderbird will send and receive mail, but new events and contacts created on the device will stay in a local, iCloud or Google book unless you also add ActiveSync, CalDAV/CardDAV, or the vendor’s own app.
Notes on each provider
Thexyz
Current Thexyz Email (the service you sign into at mail.thexyz.com) documents IMAP, SMTP, ActiveSync, CalDAV and CardDAV. Calendar and contact sync, plus ActiveSync push, are packaged as a paid Sync Upgrade. Thexyz’s Sync Upgrade page, checked November 14, 2026, listed it at $2 USD per month (about $3 CAD). Mail continues to work over IMAP and SMTP without the upgrade. Once the upgrade is on, the client area and Webmail show the account-specific ActiveSync, CalDAV and CardDAV URLs. The public knowledgebase lists example hostnames; your live URLs may use your own service identifier rather than the sample thexyz--com names.
Thexyz also still documents Thexyz Classic Email (webmail.thexyz.com), with ActiveSync at mobilesync.emailsrvr.com. That Classic settings table does not list CalDAV or CardDAV. If you are on Classic, confirm with Thexyz which product you have before you plan around all three protocols. For mail-only setup in Thunderbird, see the Thexyz IMAP and SMTP settings for Thunderbird guide.
Microsoft 365, GoDaddy Microsoft 365 and Intermedia
Exchange Online supports Exchange ActiveSync for email, calendar, contacts and tasks. Administrators can disable it per mailbox and apply mobile device policies. Microsoft does not document native CalDAV or CardDAV for Exchange Online. The supported programming interface for calendar and contacts is Microsoft Graph. Microsoft support replies have also stated that Office 365 does not support CalDAV natively. Third-party bridges exist, but they are not a Microsoft feature.
GoDaddy’s Microsoft 365 email uses the same Exchange model. GoDaddy’s iPhone instructions tell you to add the account as Microsoft Exchange (server outlook.office365.com if you have to enter it manually). Intermedia’s hosted Exchange documents ActiveSync as a per-user service in HostPilot. No Intermedia CalDAV or CardDAV articles were found.
Google Workspace
Google still publishes a CalDAV API and a CardDAV interface for Google Calendar and Contacts. Connections must use HTTPS and OAuth 2.0; basic username-and-password login is rejected. That matters for older phone profiles and some desktop clients that cannot do OAuth.
Google Sync, which used Microsoft Exchange ActiveSync 12.1 so that an iPhone could add Gmail as an Exchange account, is retired. Google says Google Workspace accounts no longer support Google Sync as of May 1, 2025 (Google Accounts more broadly, March 14, 2025). Use the Gmail, Calendar and Contacts apps, or a client that can do OAuth for IMAP, CalDAV and CardDAV.
Zoho Mail
Zoho documents all three. ActiveSync (“Zoho Sync”) can sync mail, the default calendar, contacts, tasks and notes, but Zoho states it is exclusively for business-paid plans, not personal accounts, and an administrator has to enable it for the user. Zoho also notes that ActiveSync is not supported by Outlook for Mac or Apple Mail on macOS. CalDAV is documented for Apple Calendar, Thunderbird, eM Client and others; some calendar types (shared, group, subscribed) have paid-plan limits. CardDAV is documented for Zoho Contacts, with region-specific URLs and app-specific passwords when 2FA is on.
Fastmail
Fastmail officially supports two-way CalDAV and CardDAV, plus IMAP, SMTP, JMAP and WebDAV. You must use an app password, not your regular Fastmail password. Basic plans do not include IMAP, SMTP, CalDAV or CardDAV — those users are limited to the Fastmail website and official app. Fastmail’s server documentation does not list an ActiveSync host. We did not find a separate Fastmail help article that says “ActiveSync is not supported” in those words, but ActiveSync is absent from the official protocol list.
Proton Mail
Proton Mail is built around end-to-end encryption and its own apps. Proton Mail Bridge, available on paid plans, runs on macOS, Windows and Linux and exposes local IMAP and SMTP so Outlook, Thunderbird or Apple Mail can send and receive mail. Bridge is not available on phones, and it does not provide ActiveSync, CalDAV or CardDAV. Proton Calendar can import ICS files and subscribe to external calendar URLs (read-only). Official Proton Calendar and Contacts help does not offer CalDAV or CardDAV server settings.
mailbox.org and Posteo
mailbox.org documents Exchange ActiveSync as well as CalDAV and CardDAV (https://dav.mailbox.org). Its current plan comparison lists calendar, contacts and synchronisation with mobile devices on Light, Standard and Premium. mailbox.org recommends CalDAV and CardDAV for people who prefer open standards, and it notes ActiveSync only syncs recent mail (up to 18 months on mailbox.org). With 2FA and app passwords, use app.mailbox.org.
Posteo’s feature list and help document CalDAV (port 8443) and CardDAV, with app passwords. Those official pages do not list ActiveSync or Exchange setup. On Android and in Outlook, Posteo says CalDAV needs a third-party app.
IONOS, Rackspace, Zimbra-based hosts and Kolab Now
IONOS Mail Business documents ActiveSync for mail, contacts, tasks and appointments, CalDAV for the Mail Business calendar, and CardDAV for contacts (for example dav.mailbusiness.ionos.co.uk on the UK help site; the hostname follows the IONOS region). The setup articles specify a Mail Business mailbox. Official equivalents for IONOS Mail Basic were not found.
Rackspace Email Plus documents Mobile Sync, which synchronises email, contacts and calendar events, and states that the service is available only to Email Plus users. Standard Rackspace Email is directed to ordinary IMAP/SMTP mobile setup. Official Rackspace documentation searched for this article did not include CalDAV or CardDAV endpoints.
Zimbra documents IMAP, CalDAV, CardDAV and Exchange ActiveSync (Zimbra Mobile) for iOS, Android and third-party ActiveSync clients. Advanced mobile sync is listed among commercially licensed Network Edition features, so a Zimbra-based host may or may not include ActiveSync depending on the edition and plan. Check that host’s own docs rather than assuming every Zimbra mailbox has all three.
Kolab Now documents CalDAV and CardDAV at apps.kolabnow.com, and ActiveSync for mail, contacts, calendars and tasks. ActiveSync is only available with the full Groupware option, and Kolab Now currently does not let you use 2FA and ActiveSync at the same time.
iCloud+ with a custom domain
An iCloud+ subscription can add a custom email domain to iCloud Mail, so addresses such as you@yourdomain.com are still iCloud Mail. Calendar and Contacts sync automatically on Apple devices signed into that Apple Account. Apple devices also support adding third-party CalDAV, CardDAV and Exchange accounts, but iCloud Mail itself is not an Exchange ActiveSync service. We could not find a current Apple Support page that publishes CalDAV or CardDAV server hostnames for connecting iCloud to Thunderbird or other third-party clients, so treat those setups as unofficial unless Apple documents them for your app.
How to choose
Start from the devices you actually use, then confirm the plan you would buy includes the protocol — several hosts put ActiveSync, or even CalDAV, behind a paid tier or add-on.
- Mostly iPhone, iPad and Mac: Native CalDAV and CardDAV are usually the cleanest fit, alongside IMAP for mail. ActiveSync also works on iOS if you add the account as Exchange, which can be simpler because mail, calendar and contacts arrive in one setup. On a Mac, do not assume ActiveSync will work in Apple Mail; some providers say it will not.
- Outlook on Windows: Native ActiveSync or a full Exchange/Microsoft 365 account is the path of least resistance. For a CalDAV/CardDAV host you will need a plugin, or you can use IMAP for mail only and keep the calendar in another app.
- Thunderbird, Evolution or other Linux/desktop open-source clients: Prefer a host with CalDAV and CardDAV (and IMAP). ActiveSync support in these clients is uneven.
- Android: Many mail apps can add an Exchange/ActiveSync account. For CalDAV and CardDAV, plan on a dedicated sync app. The vendor’s own mobile app (Gmail, Outlook, Proton, Zoho, Fastmail) is sometimes easier than any of the three protocols.
- A mixed fleet (some Apple, some Outlook, some Thunderbird): A host that offers all three — Thexyz with the Sync Upgrade, Zoho Mail on a business-paid plan, mailbox.org, Kolab Now Groupware, IONOS Mail Business, or a Zimbra host that includes Zimbra Mobile — lets each person use the protocol their client speaks best. You do not have to enable all three on every device.
- Encryption-first providers: Proton’s model is its own apps plus, on paid desktop plans, IMAP/SMTP through Bridge. If you need CalDAV or ActiveSync on a phone, Proton is not the match; look at Posteo, mailbox.org or Fastmail for open-standard calendar sync, or a host that also offers ActiveSync.
Whatever you pick, use the URLs and product name from your own control panel. Sample hostnames in public knowledgebases can differ from the ones issued to your mailbox, and a “Classic” or resold Microsoft 365 account is not the same product as the vendor’s current standard mail.
Frequently asked questions
If I already have IMAP, why do I need these protocols?
IMAP synchronises mail folders. It does not synchronise calendars or address books. Without ActiveSync, CalDAV, CardDAV, or a vendor app, events and contacts you create on a phone often land in a local or iCloud book and never appear in webmail.
Can I use ActiveSync, CalDAV and CardDAV on the same mailbox at once?
Often yes, if the host offers all three. A typical split is IMAP or ActiveSync for mail, CalDAV for calendars and CardDAV for contacts — or a single ActiveSync account for all three on a phone. Avoid adding the same mailbox twice (for example Exchange and CalDAV) if that would duplicate calendars or contacts. Follow the host’s device guide.
Does Outlook support CalDAV or CardDAV?
Not natively. Outlook for Windows talks Exchange, Microsoft 365, and IMAP/SMTP for mail. To sync a CalDAV calendar or CardDAV address book you need a third-party plugin, such as Outlook CalDAV Synchronizer. Zoho and mailbox.org document that route. New Outlook may not support the same plugins as classic Outlook.
Is Google Sync (ActiveSync for Gmail) still available?
No. Google retired Google Sync for Google Accounts on March 14, 2025 and for Google Workspace accounts on May 1, 2025. Google Calendar and Contacts can still be reached with CalDAV and CardDAV if the client supports OAuth 2.0.
Which option is best for an iPhone?
If the host offers ActiveSync, adding the account as Microsoft Exchange is usually the fewest steps and syncs mail, calendar and contacts together. If you prefer open standards, or the host has no ActiveSync, add IMAP for mail plus CalDAV and CardDAV (iOS has all three built in). Download a configuration profile from the host if they provide one, as mailbox.org does for ActiveSync.
What about tasks and notes?
ActiveSync often includes tasks, and sometimes notes, but support varies by server and by the phone’s app. CalDAV sometimes includes tasks (VTODO); Google’s CalDAV documentation, for example, says it does not support VTODO. Do not assume task sync just because calendar sync works. Check the host’s client list.
Are there prices attached to these protocols?
Often, yes, even when the protocol itself is “supported.” Examples we could verify: Thexyz bundles all three in a paid Sync Upgrade; Zoho limits ActiveSync to business-paid plans; Fastmail omits CalDAV and CardDAV from Basic plans; Rackspace limits Mobile Sync to Email Plus; Kolab Now limits ActiveSync to Groupware; Proton Bridge is paid and desktop-only. Always confirm on the provider’s current plan page before you buy.
Sources
- Thexyz: Contact & Calendar Sync Upgrade — ActiveSync, CalDAV and CardDAV in the paid Sync Upgrade, with the listed monthly price as of this check.
- Thexyz Knowledgebase: Email Server Settings — IMAP, SMTP, ActiveSync, CalDAV and CardDAV for current Thexyz Email, and ActiveSync (Mobile Sync) for Thexyz Classic Email.
- Thexyz Knowledgebase: Sync Thexyz Email Calendar with Microsoft Outlook using CalDAV — Outlook needs a CalDAV plugin.
- Microsoft Learn: Exchange ActiveSync in Exchange Online — ActiveSync is enabled by default and syncs email, calendar, contacts and tasks.
- Microsoft Learn: Microsoft Graph Outlook API for mail, calendars and contacts — official API path, not CalDAV or CardDAV.
- Microsoft Community: Office 365 does not support CalDAV natively (support reply, October 16, 2023).
- Microsoft Q&A: Outlook does not support CardDAV (support reply, February 2025).
- GoDaddy Help: Update email settings to Exchange on iPhone or iPad — Microsoft 365 from GoDaddy is set up as Exchange.
- Intermedia: How do I enable ActiveSync service for a user?
- Google Workspace Help: What is Google Sync? — Google Sync (ActiveSync 12.1) no longer supported for Workspace as of May 1, 2025. Page last updated November 10, 2026.
- Gmail Help: Transition your account off Google Sync — Google Accounts stopped supporting Google Sync on March 14, 2025.
- Google Calendar: CalDAV API Developer’s Guide — CalDAV over HTTPS with OAuth 2.0 only.
- Google People API: Manage contacts with the CardDAV protocol — CardDAV over HTTPS with OAuth 2.0 only.
- Zoho Mail Help: Access using Exchange ActiveSync — business-paid plans only; admin enablement; not Outlook for Mac or Apple Mail on macOS.
- Zoho Calendar Help: Setting up CalDAV sync.
- Zoho Mail Help: Sync contacts with CardDAV and Zoho Contacts: CardDAV.
- Fastmail Help: Server names and ports — CalDAV and CardDAV; Basic plans excluded.
- Fastmail Help: App passwords — Basic plans have no IMAP, SMTP, CalDAV or CardDAV.
- Fastmail API Documentation — listed protocols are JMAP, IMAP, SMTP, CardDAV, CalDAV and WebDAV.
- Proton: IMAP, SMTP and POP3 setup — Bridge is paid, desktop-only, and provides IMAP and SMTP.
- Proton: Introduction to Bridge.
- Proton Calendar Support — no CalDAV server settings; ICS subscribe is read-only.
- mailbox.org Knowledge Base: Exchange ActiveSync.
- mailbox.org Knowledge Base: CalDAV/CardDAV review.
- mailbox.org: price plans — calendar, contacts and mobile synchronisation listed on Light, Standard and Premium.
- Posteo: table of features — CalDAV and CardDAV; no ActiveSync entry.
- Posteo Help: calendar synchronisation (CalDAV).
- Posteo Help: address book synchronisation (CardDAV).
- IONOS Help: Using Mail Business on mobile devices (ActiveSync).
- IONOS Help: Syncing Mail Business calendar with macOS (CalDAV).
- IONOS Help (UK): Syncing Mail Business contacts with macOS (CardDAV).
- Rackspace Docs: Set up Mobile Sync — Email Plus only.
- Zimbra FAQs — ActiveSync, CalDAV and CardDAV on the platform; commercial features include large-scale mobile sync / Network Edition ActiveSync.
- Kolab Now: Onboarding — ActiveSync requires Groupware and cannot be combined with 2FA.
- Kolab Now: Generic CalDAV / CardDAV setup.
- Kolab Now: iPhone ActiveSync client setup.
- Apple Support: What is iCloud+? and Import existing emails to your custom iCloud Mail address.
- Apple Support: Use standards-based services for Apple devices — iOS/macOS can connect to IMAP, CalDAV, CardDAV and Exchange; this is about Apple devices, not iCloud server endpoints.
Last checked November 14, 2026. Provider features and plan limits change; confirm against the official pages above before you buy or migrate.
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