I have a server named by example myserver and main domain is mydomain.com, the complete server name is mysever.mydomain.com, I have many domains in this server like userdomain.com

The problema is that all emails that send trought of client email like MS Outlook have Field From the follow form:

From: myserver@mysrver.mydomain.com in name to user@userdomain.com

All domains have this problem, some know why is this? or were I can change this? because this is a problem all user with domains hosted in my server

This problem is with email client MS Outlook

This sounds like a problem I have seen with Cpanel. If you are using Cpanel on your server, you can fix the problem by logging in to WHM as root. Use the Exim Configuration Editor command to disable the option that reads Always set the Sender: header when the sender is changed from the actual sender. (Unchecking this will stop "On behalf of" data in Microsoft® Outlook, but may limit your ability to track abuse of the mail system.)

I hope this helps

I think tha is the problem, all is ok now! Thanks a lot