Connect Tymeslot to an on-premises Microsoft Exchange Server over Exchange Web Services. Covers the EWS endpoint, domain logins versus mailbox addresses, self-signed certificates, and how bookings are written back to your mailbox.
An on-premises
Exchange Server (2016, 2019 or Subscription Edition) reachable over HTTPS
The EWS endpoint URL, which almost always ends in
/EWS/Exchange.asmx
A login your server accepts for Basic authentication: either your email address or a
DOMAIN\username
login
The mailbox address
whose busy time should block your booking page; it is separate from the login, as step 2 explains
Exchange or Outlook: which one do I need?
Tymeslot has two Microsoft calendar integrations, and they cover different products. Pick by where your mailbox lives, not by which client you use to read it.
Exchange (this page)
is for a server your organisation runs itself. It speaks Exchange Web Services with a username and password.
Outlook Calendar
is for Microsoft 365, Exchange Online and personal Outlook.com accounts. It signs in with Microsoft and speaks the Graph API. If Microsoft hosts your mailbox, use that one: this integration will not reach it.
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What this integration does
An Exchange mailbox works like every other calendar Tymeslot connects to: it blocks your availability, and it can be the calendar your confirmed bookings are written to.
It blocks your availability
Meetings in your Exchange mailbox remove the matching times from your booking page, and appear on your Tymeslot dashboard calendar.
It receives bookings
A confirmed booking is added to your mailbox as an appointment, and rescheduling or cancelling in Tymeslot updates or removes it there.
Invitations still come from Tymeslot
The appointment Tymeslot creates carries no Exchange attendees, so your server never emails your invitee a second invitation on top of the one Tymeslot already sent. The invitee's name and address are written into the appointment's description instead.
1
Find your EWS endpoint
The endpoint is the same for every mailbox on the server and follows this pattern:
https://mail.example.com/EWS/Exchange.asmx
Replace
mail.example.com
with the hostname you use for Outlook Web App. If you are unsure, your Exchange administrator will know it; it is the same URL Outlook itself uses for Autodiscover.
The path matters
A URL that stops at the hostname, or points at /owa, will not work. Tymeslot reports
"EWS endpoint not found"
when the address it was given is reachable but is not an EWS endpoint. The usual cause is a missing
/EWS/Exchange.asmx
suffix.
Self-hosting Tymeslot on that same network is the exception.
A host that resolves to a private address is refused by default, as protection against
server-side request forgery. Set
ALLOW_PRIVATE_IPS_FOR_CALENDAR=true
on your Tymeslot deployment to permit an Exchange server on an internal network. This applies to
self-hosted installs only. On the managed service at tymeslot.app our servers have no route
to your network, so a private address cannot work there whatever you configure.
2
Prepare your login and mailbox address
The form asks for these separately, and on many servers they are not the same string.
Username and password
Whatever your server accepts for Basic authentication. On many deployments that is your email address; on others it is a domain login such as CONTOSO\alice. If you can sign in to Outlook Web App with it, it will work here.
Mailbox address
The SMTP address of the mailbox, such as alice@contoso.com. Exchange needs a real address to answer a free/busy question, and a domain login is not one. That is why the form asks for it even when it repeats the username.
Internal-only domains are fine
Tymeslot does not require the mailbox domain to be a public one. Addresses ending in .local,
.corp
or .internal
are accepted, because on-premises mailboxes routinely use them.
3
Add the calendar in Tymeslot
1
Go to [Dashboard]
→ [Integrations]
→ [Calendars].
2
Click [Connect a calendar]
and pick the [Microsoft Exchange]
card.
3
Enter the EWS endpoint, your username and password, and the mailbox address. Leave
Verify the server's TLS certificate
ticked unless step 4 applies to you.
4
Click [Discover calendars]. Tymeslot lists the calendar folders it found in the mailbox. Tick the ones you want on your dashboard and click [Add Integration].
The Exchange form: EWS endpoint, login, mailbox address, and the TLS verification switch.
Folder selection does not narrow your busy time
Exchange answers free/busy questions for a whole mailbox, not per folder. The folders you tick control what appears on your Tymeslot dashboard calendar; your availability is blocked by everything in the mailbox either way. If you keep genuinely unrelated appointments in a separate Exchange calendar, they will still remove times from your booking page.
4
Self-signed or internal-CA certificates
Plenty of on-premises Exchange deployments present a certificate issued by an internal certificate authority, or a self-signed one. Tymeslot refuses those by default, the same as any HTTPS client would.
If the connection test reports a certificate problem, untick
Verify the server's TLS certificate
on the connection form. The connection stays encrypted; Tymeslot stops checking who signed the certificate.
Prefer a trusted certificate where you can
Turning verification off means a machine positioned between Tymeslot and your Exchange server could present its own certificate and read the traffic, credentials included. On a private network you control this is usually an acceptable trade. Across the public internet, install a certificate from a trusted authority instead.
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Troubleshooting
"Authentication failed"
The server rejected the username or password. Try the other login form: if you used your email address, try DOMAIN\username, and the other way round. Tymeslot signs in with Basic authentication only, so a server that accepts only NTLM or Kerberos rejects every attempt; your administrator would need to enable Basic authentication on the EWS virtual directory.
"EWS endpoint not found"
The URL was reachable but is not an EWS endpoint. Check it ends in /EWS/Exchange.asmx.
A certificate error
See step 4. Tymeslot distinguishes a refused certificate from an unreachable server, so if the message names the certificate, the network path is fine and the fix is the verification checkbox.
Connected, but no events appear on the dashboard
Tymeslot starts the first sync as soon as you connect, but it takes a moment to finish; after that, Exchange is synced every 30 minutes. If the calendar is still empty after a few minutes, confirm you ticked at least one folder, and that the mailbox address is the one holding the appointments.
The connection is refused from a private network
A server on a private address is refused by default. See the note in step 1; this applies to self-hosted installs only.
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Frequently Asked Questions
Does this work with Microsoft 365 or Exchange Online?
No, and it should not be used for one. Microsoft is retiring the EWS endpoint for Exchange Online, so a Microsoft-hosted mailbox belongs on the Outlook Calendar integration, which uses the Graph API and signs you in with Microsoft. This integration is for servers your organisation runs itself.
Which Exchange versions are supported?
Exchange Server 2016, 2019 and Subscription Edition. Older versions expose EWS as well and may work, but they are not tested. Any server presenting a standards-compliant EWS endpoint with Basic authentication has a good chance of connecting.
Which folder do my bookings go into?
The calendar folder you choose as the meeting type's Booking Destination, in the meeting type settings. Exchange does not report which folders your account may write to, so if you choose one it cannot write to, the first booking sent there fails.
Do recurring meetings block every occurrence?
Yes. Tymeslot asks Exchange for your busy time directly rather than inferring it from the individual meeting entries, which is what makes a weekly stand-up block every week rather than only the first. Your dashboard calendar may show the series once while your booking page correctly blocks each occurrence.
Does my administrator need to change anything?
Usually not. EWS is enabled by default on a standard Exchange installation. Two policies can get in the way: EWS access restricted by throttling or client-access rules, and Basic authentication disabled on the EWS virtual directory. Both are things your Exchange administrator can check.
Can I connect a shared or resource mailbox?
Only if you have credentials that authenticate directly to that mailbox and its address is the one you enter as the mailbox address. Tymeslot does not currently authenticate as one account to read another account's mailbox.
Connect Tymeslot to Google Calendar. Busy, Tentative and Out of Office events all block bookings, so you are never double-booked, and every booking is added to your calendar.
Sync Tymeslot with Outlook Calendar via Microsoft Graph. Your Outlook events block conflicting bookings and every booking is added to your calendar. Works with Outlook.com and Microsoft 365.
Sync Tymeslot with CalDAV calendars: Nextcloud, Radicale, Baikal, Zimbra, mailbox.org, iCloud and Fastmail. Conflict checks and new bookings work without a Google or Microsoft account.
