Hi jorge11,
Welcome to the forum.
Have you attempting to remove and reset your email account [ especially if you're using imap protocols ].
In the past [ albeit several years ago now ] some of the servers with XTRA who were using Yahoo servers had problems providing identical UIDs rather than incrementing them. That turned out to be a bug that ultimately was repaired on the ISP end, but a work around was to remove the account then set it up again to force a new UID which allow the email applications to startup and sync correctly.
Note: By remove account, I do not meant to delete it off the ISP website, but remove it from your Windows phone.