Inconsistent multi-select behavior in Conversation View (Group by Conversation) in Outlook

Question

Dear support team,

We have web add-in in Outlook and we are implementing sending multiple emails to some other system.

When interacting with emails inside a conversation, the selection behavior differs depending on how the emails are selected.

Steps to reproduce:

1. Enable Conversation View (Group by Conversation)
2. Locate a conversation with multiple replies
3. Try the following scenarios: Scenario A:
   • Click on a single email that is conversation → Only that specific email is selected which is by default latest reply which contains all previous replies (expected behavior)
   Scenario B:
   • Select (check) a single email using checkbox → Only that email is selected, again latest reply (expected behavior)
   Scenario C:
   • Select multiple emails where at least one belongs to a conversation → Entire conversation (all replies) gets selected automatically. In this case if we have 1 conversation with 4 replies and 1 single email, clicking on 2 emails we will have 5/5 emails selected for sending actually which is not expected from our perspective.

Only explicitly selected emails should be included in the selection, regardless of conversation grouping. Selecting one item from a conversation should not implicitly select all replies.

Could you please provide information is this a bug or unintended UX inconsistency?

Kindest regards,

Andjela

Answer 1

In Conversation view this behavior is by design and is documented as part of the item multi‑select feature and its limitations for Outlook add-ins.

Key points from the documented behavior:

1. Item multi-select only supports messages within an Exchange mailbox and is Conversation‑view aware. When Conversations view is enabled, selection can include additional items beyond those explicitly clicked.
2. When multiple messages in a conversation stack are selected, “all chosen messages in the same conversation are included in the selection,” even if some are in different folders, as long as they are part of that conversation and the view is expanded.
3. In collapsed Conversation view, Outlook on the web and the new Outlook on Windows select all messages in the conversation stack when the conversation header is selected, including messages in other folders.
4. There is also a hard limit of 100 messages in a multi-select operation.

From an add-in perspective, this means:

• The add-in receives the selection as Outlook defines it in Conversation view, not just the items explicitly clicked.
• When a user selects multiple items and at least one is part of a conversation, Outlook may expand the selection to include all messages in that conversation, which is consistent with the documented “Multi-select in conversations” behavior, not treated as a bug.

If the desired UX is to process only explicitly clicked items, the add-in must apply its own filtering logic over the selected items it receives (for example, by ignoring additional items beyond those the add-in wants to treat as “explicitly selected”), but Outlook’s underlying selection behavior in Conversation view is working as specified.

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References:

• Activate your Outlook add-in on multiple messages