[Users] I can receive mail but not send

[Charles E. Blair]

   I have been using claws-mail for several years.  After
I changed the server used for sending mail, receiving has
continued to work but not sending.

   When I closed claws-mail after a failure, my screen
displayed

> Warning SSL connection failed (A TLS packet with
> unexpected length was received)
> Warning couldn't start TLS session

   I reproduce below part of ./claws-mail/claws.log

   Any advice on how to fix things would be appreciated.

[11:12:41] * message: Account 'c-blair at imap.illinois.edu': Connecting to IMAP4 server: imap.illinois.edu...
...
[11:12:41] IMAP4> Logging c-blair to imap.illinois.edu using LOGIN
[11:12:42] IMAP4< LOGIN completed.
[11:12:42] IMAP4< Login to imap.illinois.edu successful
[11:12:42] IMAP4< 5 OK [READ-WRITE] SELECT completed. 
[11:12:42] IMAP4- [fetching UIDs...]
[11:12:42] IMAP4< 6 OK FETCH completed. 
[11:12:42] IMAP4> 8 NOOP 
[11:12:42] IMAP4< 8 OK NOOP completed. 
[11:12:42] IMAP4> 9 UID STORE 6854 +FLAGS.SILENT (\Seen) 
[11:12:42] IMAP4< 9 OK STORE completed. 
[11:12:42] * message: Account 'c-blair at imap.illinois.edu': Connecting to SMTP server: smtp.illinois.edu ...
[11:12:42] SMTP< 220 smtp.illinois.edu Microsoft ESMTP MAIL Service ready at Mon, 13 Mar 2017 11:12:41 -0500
[11:12:42] ESMTP< 250-smtp.illinois.edu Hello [192.17.23.217]
[11:12:42] ESMTP< 250-STARTTLS
[11:12:42] ESMTP> STARTTLS
[11:12:42] ESMTP< 220 2.0.0 SMTP server ready
[11:12:42] ** warning: couldn't start TLS session
[11:12:42] *** error: Error occurred while sending the message.