Get outlook Sender properties using SentOnBehalfOfName

[Stef_99 (Mary)]

Now I use On Behalf account
but error Send outlook Mail Message : The operation failed. The messaging interfaces have returned an unknow error.

but if I remove value in On Behalf account , It working normally.

Please guide me for solve it.
Thank you.

[Christopher_R]

Hi @Stef_99

This error usually happens when the On Behalf Of address is not fully permitted or configured correctly in Outlook / Exchange. When you remove it, the email sends normally because your own mailbox has full permissions , but the delegated account doesn’t.

Below are the main checks to fix it:

1. Your admin must explicitly assign Send on Behalf permission in Exchange Admin Center:

Exchange Admin Center → Recipients → Mailboxes → (Select Mailbox) → Mailbox Delegation → Send on Behalf

Add your user account under Send on Behalf.

2. In Send Outlook Mail Message, use:

• From → Leave empty
• Sender / On Behalf Of → Put the shared mailbox or delegated mailbox

Make sure you do not put the email in the From field, because Outlook interprets it differently and can return a messaging interface error.

3. Outlook must have the delegated/shared mailbox added:

Outlook → File → Account Settings → Account Settings → Change → More Settings → Advanced → Add shared mailbox

If the mailbox isn’t visible in Outlook, UiPath cannot send emails on its behalf.

4. Some environments block “Send on Behalf” even if it is configured.

Ask admin to assign:

Mailbox → Manage permissions → Send As

Then in UiPath, set the email in the From field instead of “On Behalf Of”.

This works more reliably.

Happy Automation