When performing test on a Microsoft Exchange server, some tests will return a transaction time warning. For the most part this is not an issue and nothing needs to be done. This delay is intentional on the part of Microsoft Exchange to help prevent spam. The warnings are typically given when it takes more than 1 second for the SMTP connector to respond to the request. This process of delaying multiple mail requests is called tarpitting.
If this warning bothers you, there is a change that you can make that will fix the Transaction time warnings for Exchange 2007 and 2010.
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.
One of the most common questions we get regarding mobile devices is how to setup an Apple iPhone with access to a corporate Microsoft Exchange mail system. This doesn't have to be a local system, it could be a hosted cloud Exchange server as well. Many people often will use a POP connection but this really doesn't allow the mobile device to exploit the full capabilities of the Microsoft Exchange services such as synchronizing contacts and calendars. So, get the full benefit of Microsoft Exchange by using the Exchange mail connector on the mobile device.
There are a couple of pre-configuration steps that you may want to take, especially if you have moved your Exchange service to a different hosting provider.