Unfortunately, theré's this language barrier for me as Foxmail's site is in Chinese and I don't know any Chinese, so I can't access the support pages.
Can you send mail with another mail client? If so, could you show the smtp settings for that client?
Apparently TB first sends an EHLO command and afterwards a HELO command, it shouldn't do that HELO command if the server at smtp.foxmail.com responds properly.
I tried an unauthenthicated contact with that server and over here I get this:
[12:05:41] C: Connected to smtp.foxmail.com, port 25
[12:05:42] S: 220 smtp.foxmail.com ESMTP Foxmail Ver 1.0
[12:05:42] C: EHLO Basilisk
[12:05:42] S: 250-smtp.foxmail.com
[12:05:42] S: 250-PIPELINING
[12:05:42] S: 250-SIZE 52428800
[12:05:42] S: 250-AUTH LOGIN
[12:05:42] S: 250-AUTH=LOGIN
[12:05:42] S: 250 8BITMIME
[12:05:42] C: MAIL FROM:<forget about the address> SIZE=381
[12:05:43] S: 503 Error: need EHLO and AUTH first !

Your connection gets broken and you aren't getting any responses, so off hand my guess would be a virus scanner or a firewall that's interfering with the connection.
You could enable protocol logging for smtp and try to send a message and afterwards post that log.
Enabling protocol logging is at the account properties, left of the transport option you see a +, click on that and you get an extra menu option.