If you're missing an e-mail that you're expecting from a sender there are several locations in which you may want to search. The first step is to check your entire mailbox for the message. To do this in outlook, type some text into the Search box near the top of your inbox and change the drop down to "all mailboxes". 
To search by sender, you may select the "from" option from the ribbon at the top. But as shown in the screenshot, there are several options with which to search by. 
"Subject" allows you to search by e-mail subject/title, "Has Attachments" allows to search by attributes of an attachment on the e-mail. Use these indicators to see if you can find the e-mail anywhere in your mailboxes.
If the e-mail does not show up anywhere, the next step would be to make sure it's not being quarantined. To search quarantined messages, follow the directions outlined here: https://uwyo.teamdynamix.com/TDClient/1940/Portal/KB/ArticleDet?ID=17132.
If you have searched quarantined messages to no avail, check to see if the mail is in your "recover deleted items" folder.
To check this, go to https://mail.uwyo.edu and log in.
Click on the deleted items folder in your navigation pane.
At the top of your deleted items should be an option to "Recover deleted items from this folder". Click this option to bring up your recently deleted items over the last 30 days.
If the mail is in your recover deleted items, select the mail or several mails by holding down ctrl and selecting the e-mail, then click "restore". This will return the e-mail(s) back to your mailbox.