There is a campus-wide issue with email delivery using off-campus accounts and Gatorlink accounts.
UF IT has confirmed the issue with slow email delivery and submission through smtp.ufl.edu. Unfortunately, this is a result of the ongoing issue with the GatorLink email backend server and cannot be resolved until that problem is first resolved. UF IT staff will continue monitoring this situation and working to mitigate the disruption this is having to the SMTP email delivery service.
Mail that stays within the exchange system using Outlook, including Office365, will be fine but mail from off-campus accounts, Gatorlink accounts, and Thunderbird users will be slow to be delivered.