We don't support Thunderbird sorry, so I can only direct you to webmail, as we have some control over that aspect. If Thunderbird isn't functioning correctly, I have to direct you back the publisher 
If you get duplicate emails via webmail, then this will be an issue with your email address itself, which we can help with. If the duplicates only appear in your inbox using Thunderbird, it could be a failed send/receive session, drops in connection or a configuration issue, but again I can't assist with that side. There may be members of the community with a bit more knowhow than me though 
Brodie