Outlook add-ins are available on messages or appointments while composing or reading, but not other item types. Outlook does not activate add-ins (they are grayed out in ribbon bar) if the current message item, in a compose or read form, is one of the following:
The reading pane is hidden (View > Reading Pane > Hidden)
Protected by Information Rights Management (IRM) or encrypted in other ways for protection. A digitally signed message is an example since digital signing relies on one of these mechanisms.
A delivery report or notification that has the message class IPM.Report.*, including delivery and Non-Delivery Report (NDR) reports, and read, non-read, and delay notifications.
A draft (does not have a sender assigned to it), or in the Outlook Drafts folder.
A .msg or .eml file is an attachment to another message.
A .msg or .eml file is opened from the file system.
In a shared mailbox, in another user's mailbox, in an archive mailbox, or in a public folder.
👉 Update, see this article to check if your Outlook supports add-ins for shared mailboxes
Using a Custom Form.
Learn more below.
Desktop Outlook Users
If you're using desktop Outlook, Microsoft only displays the add-in while you are viewing an email.
With Reading Pane Off
If you have turned off the reading pane (View > Reading Pane > Off) then the CloudExtend add-in will only be visible from the Messages tab on the ribbon bar when an individual email is open.
With Reading Pane On
Most users use the reading pane (View >Reading Pane > Right or Bottom). With the reading pane on the CloudExtend add-in will always be available from the Home tab on the ribbon bar.
Outlook Add-In is grayed out
Outlook Add-Ins are greyed out when the reading pane is hidden and a mail is not in open state. To activate add-ins either turn on the reading pane by (1) clicking View, (2) select Reading Pane, and (3) choose Right or Below.
Outlook Web Access Users
If you're using Outlook Web Access (OWA) to get your email the CloudExtend icon will appear at the top right of your email near the reply/forward icons. If it's not there you may also find it by clicking the 3 dots at the top right.
Follow the steps below if you always to see it at the top right of your email.
Step 1: At the top of the page, select Settings > View all Outlook settings.
Step 2: Select Mail > Customize actions.
Step 3: Select the checkboxes for CloudExtend.
Step 4: To change the order in which they appear, select them in a different order.
Step 6: Select Save.