How can we force a mailbox item to be persisted to EWS?

问题

Note: This particular issue has significant impact on our customers, which translates to high business impact with direct consequences on revenue.

TL;DR.

How can our Office add-in for Outlook, when a user interacts with our add-in while composing an email draft, minimize the amount of time it takes before the EWS GetItem API will return an OK response for the itemId we receive from Office.context.mailbox.item.saveAsync()?

If it turns out that our add-in has no control over when the item will be persisted to EWS, then what could an end-user do to speed this up?

We are looking for either (a) a technical solution, or (b) messaging to instruct our customers on how to mitigate/fix/work around this issue.

End-User Impact

Some of our customers are unable to send emails using our Office add-in for Outlook, or have to wait an exceedingly long time (> 2 minutes) before their email will send.

Our Goal

We want all of our customers to be able to send emails using our add-in, without having to wait for an unreasonable amount of time.

Additional Context

Based on our logs and customer reports, this issue only exists in the Outlook 2016 for Windows desktop application. We have no evidence to suggest the issue is present in any other version of Outlook, including Outlook 2013 or Outlook for Mac, however it is possible that the issue may be present in those clients as well.

Overview of our add-in

Our add-in integrates with Compose mode to provide additional functionality while composing email messages, such as templates, follow-ups, open and click tracking, and scheduling.

Our add-in works in tandem with our SaaS product like this:

1. Our add-in sets EWS extended properties on the email message with metadata indicating which features are enabled on that message.

2. Our SaaS product, out of band, is configured to read from the customer's mailbox via the EWS API. When it encounters EWS extended properties our Office add-in has written, it triggers the code paths to satisfy the desired behavior.

Root Cause Analysis

The root cause of our problem is our interaction with EWS in Outlook 2016 for Windows. In order to successfully interact with EWS to read/write to a mailbox item, it must be aware of that item.

The documentation for Office.context.mailbox.item.saveAsync() says:

In Outlook Web App or Outlook in online mode, the item is saved to the server. In Outlook in cached mode, the item is saved to the local cache.

It goes on further to say:

Note: If your add-in calls saveAsync on an item in compose mode in order to get an itemId to use with EWS or the REST API, be aware that when Outlook is in cached mode, it may take some time before the item is actually synced to the server. Until the item is synced, using the itemId will return an error.

Thus, we have concluded that Office.context.mailbox.item.saveAsync(), although it does indeed return an eventually valid itemId, does not guarantee that any subsequent EWS interaction will succeed. So far, we have found no way to accelerate the process of the Outlook client actually making EWS aware of the mailbox item.

Mitigation

We have attempted to mitigate this problem by polling EWS GetItem to attempt to obtain a ChangeKey for the item with the itemId we receive from Office.context.mailbox.item.saveAsync(). While we have seen that this does eventually succeed, it may take a minute or longer before this occurs. That is simply far too much time for our customers to have to wait.

Understanding "online mode" vs "cached mode"

If the Outlook 2016 for Windows desktop client is in "cached mode", is there anything the user can do to:

1. …know whether the client is in "cached mode" or "online mode"?
2. …attempt to force the client into "online mode"?

回答1:

There is no way to speed this up in cached mode. Unfortunately this is a limitation of saveAsync in compose mode. Some things of note:

1) The EWSId is only valid while the item is a draft. After it is sent, when the item is in sent items, it will have a new EWSId which is not obtainable from the Office.js

2) Could you save your information into the custom properties, instead of the EWS Extended Properties. (Office.context.mailbox.item.customProperties) https://dev.office.com/reference/add-ins/outlook/1.5/CustomProperties?product=outlook

These properties will be saved to the mail in the sent item, but will NOT be transmitted. Then could you find those properties

These are stored as a JSON dictionary on the item in Key/Value pairs. The name of the mapi property is "cecp-[extension id from manifest]" (in PS_PUBLIC_STRINGS)

https://msdn.microsoft.com/en-us/library/office/cc842512.aspx

3) It does kind of sound like a better way to solve this would be an Office.js function that gives write access to this? (though we don't completely understand your scenario). Request for new features should go through UserVoice:

https://officespdev.uservoice.com/forums/224641-general/category/131778-outlook-add-ins.

4) Being in Online Mode would greatly mitigate the time. A User can know whether or not he or she is in online mode, but an Add-in cannot.

https://support.office.com/en-us/article/Turn-on-Cached-Exchange-Mode-7885af08-9a60-4ec3-850a-e221c1ed0c1c

Additionally, the status bar will say "Connected to Microsoft Exchange" in cached mode, and "Online with Microsoft Exchange" in online mode.

Switching to Online mode, removes a lot of the benefits that cached mode has. Cached mode is default in Outlook 2016.

来源：https://stackoverflow.com/questions/46671562/how-can-we-force-a-mailbox-item-to-be-persisted-to-ews