Copied from : https://stackoverflow.com/questions/46671562/how-can-we-force-a-mailbox-item-to-be-persisted-to-ews?rq=1

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:

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

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:

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

Hello,

I’m working on a web add-in for Microsoft Outlook, and I’ve run into a few issues with Office.js’s body.setAsync() method.

I’ve posted two questions to Stack Overflow related to my add-in’s use of the body.setAsync() method:

- Base 64 signature images in the Outlook Web App are lost when I try to update the body of an email [link: https://stackoverflow.com/questions/51736434/how-to-prevent-base-64-format-signature-images-being-dropped-in-outlook-web-app]

- Getting the email body with body.getAsync() and then setting it with body.setAsync() causes line spacing issues in desktop Outlook platforms that use Word as the text editor [link: https://stackoverflow.com/questions/51603265/line-spacing-increased-issue-when-updating-email-body-with-office-js]

My add-in needs to add content to the end of the email, and looking at the methods available to us on the body object in office.js, it looks like using body.setAsync() to replace the entire email body is the only way I can reliably add new content to the end of the email.

We know there is a body.prependAsync() method already and would like to request a body.appendAsync() method that added content to the end of the existing email body. This would solve the issue I’ve been having with dropped signature images. Being able to append content to the end of an email would also allow me to avoid the line spacing issue because I wouldn’t have to reset the entire body content of the email.

If there are no plans to add a body.appendAsync() method, is there any other workaround you’d suggest for adding content to the end of an email without us dropping Base 64 images from users’ signatures?

Thank you!