Outlook sending error message on account not set up in my compter

[iandmac]

My computer is sending a delivery error message from an old business email
account that was never set up as an email address is this comptuer. The
message is sent to the recipient of an email from me and is also sent to me.
Emails do go through but the message causes some confusion to the recipients

 

[Brian Tillman [MVP - Outlook]]

My computer is sending a delivery error message from an old business email
account that was never set up as an email address is this comptuer. The
message is sent to the recipient of an email from me and is also sent to me.
Emails do go through but the message causes some confusion to the recipients

How do you know Outlook is sending the message?