MacBook Mail: Sent replies no longer appearing with original messages in Inbox
This sounds like a possible issue with Apple Mail's Conversation View settings or the way your Sent mailbox is configured.
Since the problem occurs after clicking Send, I would try the following steps on your MacBook Pro (M1, 2020).
1. Check Conversation View
• Open the Mail app.
• Select View >> Organize by Conversation.
• Make sure it is checked.
• If already checked, turn it off and back on.
• Open an original email and look for a disclosure arrow or conversation count to see whether your reply is included in the thread.
Apple's instructions: View email conversations in Mail on Mac.
2. Check the message display order
This is particularly important because you want your sent reply to appear above the original email.
• Go to Mail >> Settings >> Viewing.
• Find Show most recent message at the top.
• Make sure it is selected.
This setting controls the order in which messages appear within a conversation.
Apple's instructions: Read and respond to emails in Mail on Mac.
3. Expand all conversations
• Open Mail.
• Select View >> Expand All Conversations.
• This ensures that all messages within a conversation are displayed rather than hidden behind a message count.
This may restore the appearance you were accustomed to, even though the sent reply is stored in Sent rather than Inbox.
4. Verify your Sent mailbox settings
• Go to Mail >> Settings >> Accounts.
• Select the affected email account.
• Click Mailbox Behaviours.
• Check that the Sent Mailbox is assigned to the correct Sent folder on your email provider's server.
Avoid changing the setting unless it is incorrectly assigned.
Apple's instructions: Change Mailbox Behaviors settings in Mail on Mac.
5. Rebuild the Inbox if messages still appear missing
If the above steps don't help:
• Select your Inbox in the Mail sidebar.
• Choose Mailbox >> Rebuild.
• Allow Mail time to synchronize and reload the messages.
Apple's instructions: Rebuild mailboxes in Mail on Mac.
One important clarification
Apple Mail normally stores sent replies in the Sent mailbox, not the Inbox.
However, Conversation View is designed to group the original incoming message and your sent reply together, allowing you to see the entire exchange from the Inbox.
Your desired result should therefore be achievable through the conversation display settings, without manually moving sent messages into your Inbox.
My recommendation: Start with Steps 1, 2 and 3 before attempting to rebuild anything.
If the problem continues, check whether it happens with all email accounts or just one (iCloud, Gmail, Yahoo, etc.). That will help narrow down whether this is an Apple Mail issue or an email-provider synchronization issue.
Also check if there are any updates to macOS Golden Gate. System. Setting >> General >> Software Update
The latest version of macOS is 27.2. Learn how to update the software on your Mac and how to allow important background updates.