Ok, I know there have been a few responses to this, but none seem to fit the exact issue I am having, so I'm going to ask again.

I have two users in particular, one on Outlook 2010 and one on Outlook 2013. They have hosted Exchange, and the Exchange server is 2007. The Exchange host provider is located in the Central Time Zone. Computers for my users are all set to correctly to Eastern Time Zone. Windows 7 and 8.1 machines with all updates installed are what the users are using. I also logged into the hosted OWA option and set the time zone to EST there as well.

When I send an invite from Outlook 2010 user to another Exchange server, meeting time in the email invite BEFORE accepting shows the correct time zone for that user, and stays correct when accepting. When I send an invite to Gmail, again, shows correct time before and after accepting. When I send to a Yahoo account, it shows the time one hour behind before accepting - essentially shows the CST time. Once I accept the meeting in Yahoo, it shows the correct time in the Yahoo calendar, but the email with the invite still shows the wrong time, one hour earlier. And obviously if the user doesn't accept the invite but just uses it as a guide, they will show up one hour earlier.

Is this an issue for Yahoo, or Exchange 2007? It might be possible to move my client from Exchange 2007 to 2010 or 2013, but I don't want to do that if it won't fix the problem.

Should be an issue with the time zone settings on all Outlook clients involved.

Has Gmail/Yahoo account mentioned here been configured into Outlook clients?

If you are using Outlook 2010 you need to use a time zone with the correct DST settings for your location. If your location does not observe DST, do not choose a time zone that does then deselect the option to automatically update for daylight saving time. You need to use a time zone that does not observe DST.

http://www.slipstick.com/outlook/calendar/meeting-requests-and-appointments-are-off-by-one-hour/