Since Dec 31, 2015 all my outgoing mail had been blocked. Has latest version 38.5.0 No bounces. All of my outgoing mail just vanished and never reached anyone. Not even reached the hosting ISP even they can see the log of failed deliveries. They informed there's a spoof spammer connecting to my outgoing mail. I receive incoming mail just find without any problem. I had been in contact with my hosting ISP. Found my webmail is working just fine. Settings for Thunderbird were same as instructed by the hosting ISP. Computer checked for any hidden virus or malware, none found.