On day the Send To option lost the Mail Recipient option from a clients Windows 7 system. The client was using Outlook 2010 and the typical solutions posted that suggested creating a new Mail Recipient didn't work.
The following solution did work for our client.
After completing several updates on Exchange 2013 due to another issue, we found that e-mail messages were going to the Drafts folder instead of the Sent Items folder. In addition the server was not receiving any messages either.
After further investigation we found that the Mail Transport service was failing, not immediately, which was why we didn't notice it after it was started. In this particular case the client had a secondary SMTP port configured for relay messages but that port was setup on both the Exchange 2013 CAS and Database servers but only one of the CAS server actually had the IP address assigned on the NIC. Once the relay SMTP port configuration was removed from the Database server the Mail Transport service ran fine and mail flowed through the system correctly.
A very frustrating situation for our business clients is when they send an e-mail message to a client that has hyperlinks embedded in the message and the link doesn't open in the client's web browser. The issue is typically caused when Google Chrome or another web browser is installed and then later removed. But malware applications will also cause this issue too.
To fix the web links in your Microsoft Outlook application so that they will open, follow these steps.
With such a large number of connection issues with Outlook 2016 connecting to Office 365 you would think someone would have the definitive answer to these persistent issues. It is unfortunate that the issues that plague Outlook 2016 are not all related. Hopefully after you have read this technical note you too will be able to resolve your issue. Although this is not the fix that will fix all Outlook connectivity issues, but then again it might fix yours.
I guess starting with the obvious is always a good place to begin.
The reading pane in Microsoft Outlook is a took that allows the user to quickly view the contents of an email message. The down side to this is that it causes an open message process that can cause some e-mail borne viruses to activate as soon as they enter the Inbox. For security purposes we recommend that end users review the subject and who the message is from before opening the message to ensure they are not allowing something malicious to run on their computer. Closing the reading pane helps to ensure that the end user takes the time to check the message details first before opening it.
How to Turn Off Reading Pane