Hey,
Also having trouble with bigpond on thunderbird on ubuntu 15.04, been working fine for the last 12 months or so, but just yesterday started getting the error
An error occurred while sending mail: The mail server sent an incorrect greeting: nskntcmgw07p BigPond Outbound Connection refused, too many sessions from 121.214.120.242. OB007.
Checked the ip on spamhaus.com and they reckon that it's due to not using smtp authentification, so I turned on ssl/tls for in and outcoming mail and changed the port number to 465 (also tried 587), but was getting the same error message.
Update: just sent the mail through, but it seems that it is inconsistent. Has anyone had similar experiences?
I am using mail.bigpond.com for pop and smtp server