AI offers this for Express Accounts, the forum you queried. But Express Invoice is much the same.
"You cannot reliably use Express Accounts to send through your Outlook (Microsoft 365/Outlook.com) address in a way that will make sent emails appear in your Outlook "Sent Items" folder, unless the sending process goes through Microsoft's servers in a way Outlook expects.
- Ticking the MAPI box in Express Accounts sends mail via the local MAPI client, but MAPI-sent messages are not stored in the cloud "Sent Items" unless the email client itself (e.g., Outlook) saves them there. Express Accounts does not synchronize these outbound messages with your Outlook Sent Items folder.
Using SMTP is no longer feasible for many users because Microsoft has disabled Basic Authentication and now requires OAuth2/Modern Authentication for SMTP connections. Most third-party software, including Express Accounts, does not yet support this for Microsoft accounts.
There is no evidence that Express Accounts supports OAuth2 or the newer Microsoft authentication protocols for SMTP. As a result, you cannot add your Outlook address via SMTP in a way that would place outbound mail in your Outlook "Sent Items" unless Express Accounts directly supports these protocols (which it currently does not).
To ensure sent emails appear in your Outlook "Sent Items" folder:
You must send the email through Outlook itself, Outlook Web Access, or a client that authenticates using Modern Auth (OAuth2) to Microsoft's servers and saves sent items to the server-side "Sent Items" folder.
Sending via MAPI in Express Accounts puts the item in the local client’s Sent folder, not in the server/cloud Sent Items (unless the client—Outlook, for example—synchronizes all Sent mail to the server, which is not the default for external MAPI calls).
Workarounds:
Manually BCC or CC yourself on every message you send via Express Accounts, so you get a copy in your inbox which you can then move to Sent Items manually. Or you may be able to apply a filter in Outlook to direct mail from EA to the SENT folder.
Use Outlook itself to compose or forward invoices/receipts so items are always filed in Sent Items.
Check if Express Accounts has released updates that support Microsoft's new authentication or an official Outlook integration (currently, documentation and search results show no such OAuth2 support).
In summary, current Microsoft account security (disabling Basic Auth) and the way Express Accounts operates with MAPI and SMTP make it impossible to have outgoing items from Express Accounts directly and automatically appear in your account’s Outlook Sent Items folder. You would need to use a full-featured mail client with native Modern Auth support for this feature.
File a suggestion with NCH.