Classic Outlook over MAPI
Classic Outlook for Windows connects to Exchange using the MAPI protocol over HTTPS. MailSite 11 includes its own MAPI server, so Outlook synchronizes email, calendars, contacts, tasks and notes and sends mail through one Exchange-type connection to the MailSite MAPI server, without separate account configurations for IMAP and SMTP. MAPI is an optional licensed feature in MailSite.
What Was Tested
These results are for MailSite 11.1.137, released November 4, 2026, with:
- Classic Outlook for Windows: Outlook 2021 (Office Professional Plus 2021, Current Channel), build 16.0.20326.20232, on Windows 11 Pro version 25H2 (build 26200). Microsoft 365 Apps ships the same Outlook build as Version 2608.
- Classic Outlook in Microsoft 365 Apps: Current Channel Version 2610, build 16.0.20527.20088 (released October 21, 2026)
Each item has one of three labels:
- Supported and tested
- Works, and was tested with the Outlook builds above.
- Supported with limitations
- Works, with the limits described.
- Unsupported
- MailSite doesn't provide it.
Setup and Connection
| Feature | Status | Details |
|---|---|---|
| Autodiscover and profile setup | Supported and tested | Outlook sets up the account from just an email address and password. The mailbox needs MAPI access turned on, and the server needs a MAPI license. |
| Cached Exchange Mode | Supported and tested | Outlook downloads the mailbox, receives new mail and folder changes as they happen, and can fetch older mail outside its offline window. |
| Online mode (no local cache) | Supported and tested | Mail, calendars, contacts, notes, tasks and folders all work without a local copy. |
| Reconnect after a lost connection | Supported and tested | Outlook automatically reconnects after a dropped connection and picks up where it left off, without duplicating changes. |
| Authentication | Supported with limitations | Outlook authenticates with a user name and password over HTTPS, optionally using NTLM. Alternatively, a MailSite administrator can configure MailSite to require (OAuth) authentication, which requires each Windows PC to be configured to support it. Kerberos and multi-factor sign-in are not supported. |
Mailbox Features
| Feature | Status | Details |
|---|---|---|
| Out of office | Supported and tested | Set automatic replies in Outlook or ExpressPro; both show the same settings. |
| Server-side rules | Supported and tested | Rules created in Outlook's Rules and Alerts run on the server. |
Calendars and Scheduling
| Feature | Status | Details |
|---|---|---|
| Meeting invitations and responses | Supported and tested | Send invitations, accept, decline or propose a new time, and receive updates and cancellations between MailSite users. Invitations emailed from other calendar systems, such as Google Calendar, arrive as meeting requests and can be answered too. |
| Recurring meetings | Supported and tested | Create recurring meetings and change or cancel single occurrences. Each meeting keeps its own time zone. |
| Creating calendars | Supported and tested | Create new calendars in Outlook, in Cached Exchange Mode or online mode. A calendar created inside Calendar is shown beside it, the way ExpressPro and other clients list it. |
| Free/busy lookup | Supported and tested | The Scheduling Assistant shows when other MailSite users are free or busy. |
| Resource booking (rooms and equipment) | Unsupported | MailSite does not support room or equipment mailboxes that automatically accept bookings. A mailbox can be created for a room or for equipment and users can invite it as an attendee, but someone has to respond to the invitation for it. |
Contacts
| Feature | Status | Details |
|---|---|---|
| Contacts | Supported and tested | Create, edit and delete contacts with all of Outlook's fields, photos, attached files, formatted notes and custom forms. Changes also appear in ExpressPro, on mobile devices and in other Exchange clients. |
| Custom contact fields | Supported and tested | Fields added to a contact in Outlook are kept on the server, and can be viewed, added, changed and removed in ExpressPro as well as in Outlook. Phones can't show them, as on Exchange, and editing a contact on a phone keeps them. |
| Address book lookup | Supported and tested | Look up users in Outlook's address book. Entries show job title, department, company, office phone numbers and address. Outlook also downloads the offline address book. |
Tasks and Notes
| Feature | Status | Details |
|---|---|---|
| Tasks | Supported and tested | Create, edit, complete and delete tasks with due dates, reminders, priority and recurrence, including tasks set to "Regenerate new task", where the next task is created a set time after the last one is completed. Changes also appear in ExpressPro and on mobile devices. Task notes keep their formatting, links and pictures in both directions. |
| Task assignment | Supported and tested | Assign tasks, accept or decline them, and pass a task on to one or more people, in Outlook, in Cached Exchange Mode or online mode, or in ExpressPro. Answers go to whoever most recently assigned or passed on the task, as on Exchange. |
| Notes | Supported and tested | Create, edit and delete notes, keeping their color. The same notes appear in ExpressPro, Apple Notes and on mobile devices. |
| Shared notes | Supported and tested | Share the Notes folder from Outlook or ExpressPro. Others open it with Open Other User's Folder and can edit the notes when allowed. |
| Private notes | Supported and tested | Notes marked Private are visible only to their owner, even in a shared Notes folder. |
Sharing and Delegation
| Feature | Status | Details |
|---|---|---|
| Folder permissions and delegated folder access | Supported and tested | Permissions set in Outlook are the same ones used in ExpressPro and the Console. Outlook's Author and Publishing Author roles let a person change and delete the items they created, and Nonediting Author lets them delete those items but not change them, as on Exchange. |
| Outlook Delegate Access (meeting requests sent to a delegate) | Supported and tested | Add delegates in Outlook's Delegate Access dialog to give them folder permissions, the Send on Behalf right and copies of your meeting requests. |
| Shared mailbox access | Supported and tested | Grant access to a whole mailbox, including folders created later, or folder by folder, from ExpressPro or the Console. |
| Send As | Supported and tested | A mailbox owner (in ExpressPro) or an administrator (in the Console) can let another user in the domain send as that mailbox. Messages arrive from the shared mailbox alone. The sender's own Sent Items copy shows "on behalf of". |
| Send on Behalf | Supported and tested | Granted the same way as Send As, or by adding a delegate in Outlook. Messages arrive from the other mailbox and show who sent them. |
| Shared calendars, contacts and tasks | Supported with limitations | Share folders from Outlook's Permissions tab, and they appear in the other person's Outlook automatically. Only the default Contacts and Tasks folders can be shared. |
Requirements
- A MailSite license that includes MAPI, and MAPI access enabled for each Outlook user's mailbox.
- DNS for Autodiscover: an
autodiscover.host name or an_autodiscover._tcpSRV record for each mail domain, covered by the certificate. - HTTPS (port 443) reachable from wherever Outlook is used.
Other Clients
Phones and tablets connect through ActiveSync; see mobile synchronization. macOS Mail, Calendar and Contacts use Exchange Web Services. The client compatibility guide covers the connection method for each client.
Results can change between builds. Read the release notes for the build you plan to deploy, or tell Rockliffe which Outlook workflows you depend on.