MailTips brings together information from many sources; its value to users is taking what can be complicated on the backend and presenting it very simply.
This does mean, however, that there are a few different places to look when troubleshooting MailTips. This post outlines some basic troubleshooting steps for MailTips.
A note about caches
MailTips caches data at many levels (on the server and on clients) to keep the end-user experience quick and responsive. Sometimes the only thing that's wrong is that a cache has yet to be updated. Restarting clients (like Outlook or OWA) and sometimes services (like IIS) can assist in troubleshooting. Also, group metrics only updates every night, so keep this in mind when you see group metrics based tips.
Is the problem limited to Outlook clients?
If MailTips in Outlook Web App work as expected, but Outlook 2010 is not showing MailTips, the problem might be related to Autodiscover.
Outlook uses Autodiscover to find the URL for Exchange Web Services; EWS is used to retrieve MailTips. If Autodiscover isn't working, or if the EWS URL provided by Autodiscover is incorrect, then Outlook will not be able to contact the MailTips web service.
Is the problem limited to only some MailTips?
Remember that the external senders MailTip is disabled by default. To enable it, run the following:
MailTips determines whether a recipient is internal or external by comparing the domain of the ExternalEmailAddress property (the targetAddress attribute in AD) with the list of accepted domains. In some cases we have had 'external recipient' tips appearing for internal recipients whose email was hosted on a system that wasn't in our accepted-domain list. Generally the solution is simply to add the domain to the accepted-domain list.
Other options on OrganizationConfig can disable Group Metrics-based and Mailbox based MailTips, so it's worth checking those, too.
Finally, note that automatic reply (aka OOF) MailTips are only available for recipients whose mailboxes are on Exchange 2010 mailbox servers.
Is the problem limited to Group Metrics based MailTips?
Group metrics counts the members of all groups periodically on mailbox servers, and uses Exchange File Distribution to get the group metrics files out to CAS servers.
To start, look for a file share like \\mailboxserver\GroupMetrics where your group metrics are generated. If you're not seeing that on any mailbox servers, you're not generating group metrics. By default, group metrics are generated on any server that generates an OAB; if you do not use OABs, then you will need to explicitly specify where you want group metrics to be generated with this cmdlet:
(Note that this cmdlet is only useful to organizations who do not use OABs. If a mailbox server is generating an OAB, it will also generate group metrics regardless of this setting)
When you look in that share, make sure the files in it have been changed within the past 24 hours. Restarting the Exchange Service Host will generate a fresh file; that process may take minutes or hours depending on the number of groups in your organization. Also, make sure the Exchange File Distribution service is running on Client Access servers and Mailbox servers, and that your CASes can connect to \\mailboxserver\GroupMetrics.