Outlook: Your message did not reach some or all of the intended recipients.

Had a problem with a customer today sending an email and instantly getting a response that the message was undeliverable, with the message:

Your message did not reach some or all of the intended recipients.

Subject: FW: Offer

Sent: 20/09/2011 10:33

The following recipient(s) cannot be reached:

‘user@domain.com’ on 20/09/2011 10:33
None of your e-mail accounts could send to this recipient.

This problem is caused when the email address has been pasted into to the to: field with the mailto: portion still intact.

Go into the sent items and open the email that failed to transmit and then choose “resend this message” and then double click on the email address you will probably see something like this:

As in the picture the “E-mail type:” is set to MAILTO. Clicking on the Internet type button will reset it back to SMTP and should be able to send the message.

Sometimes the incorrect address can also get cached into your NK2 file, so you will need to remove it from your autocomplete cache to make sure that you don’t get the problem again.