Cause
Various
Resolution
Solution 1
One solution to the problem is check the email address to which you're sending. Sometimes the email address may not be valid or it may be typed incorrectly. Sometimes, when typing the first letter of an email address and pressing Tab, Outlook will automatically select an old, invalid entry. It will appear to the sender to be a valid email address when it actually isn't. This can also happen when a recipient of the original message uses the "Reply All" feature. When composing your message in Outlook, delete the auto-complete entry by pressing the down arrow key and pressing Delete.
Solution 2
Another issue could be the message is corrupt. In this case, if you can still access the outgoing or queued email, try sending a new message; or copy and paste the text from the old message into a new message and send the new message. You probably will need to delete the old message from your Outbox before trying to send; otherwise the old message may keep the new message from sending.
Solution 3
If there are problems with your email provider's SMTP server, this may also cause a brief delay in sending the message. The email client software should notify you accordingly if that is the case. IT Help Central can research further if the server is a TTU server.
Solution 4
If you are using Outlook and receive the message seen below, close Outlook, wait a few seconds, and then re-open it and try again.
Solution 5
If you receive the following error, the problem can be complex to solve because many things could cause this. The problem could be client or server related, either on the sender or receiver's end. Please contact IT Help Central so that full-time staff or student supervisors can troubleshoot this issue in-depth in order to arrive at a solution.
Solution 6
If you receive the following message it may be due to TTU's junk email filtering process.
Outcome
Mail will be delivered properly.