Honestly, it's difficult to work out what you're actually trying to do, and you provide near zero details on your configuration, so all we can do is make generic stabs in the dark.
I'm assuming Thunderbird is installed in the Windows guest and you're trying to access something external on those ports (seeing as they are standard mail server ports).
It networking actually working in the guest at all - can you get to the Internet?
Do you have a firewall on the FreeBSD host? (For reasons that escape me, it's incredibly common to see posts on here from people who decided to set up a bunch of complex firewall rules they likely don't even understand *before* actually getting things working, so we don't know if it's actually a real issue, or just a mis-configured firewall. Then to top it off they don't think to just disable the firewall temporarily to rule it out)
Assuming network is working, bhyve does not limit anything. You should effectively have full layer 2 connectivity between the bhyve guest and everything else on the network it is connected to, no different to a real machine.
To actually help troubleshoot, the bhyve and networking config on the host would be useful for a start, as well as evidence of basic tests (can you ping the gateway/Internet, do dns lookups, etc)