Unable to send through Exchange SMTP after today's update

Ever since the update I installed this morning I cannot send email via SMTP any more:

Connection log (2016-11-28 17:18:56 +0000):
16:52:08 Sending request (5)
16:52:08 Handling request
16:52:08 Ready to run action (retry count: 0)
16:52:08 Clearing connection to my-smtp-host.exchange
16:52:08 Trying to connect to my-smtp-host.exchange on port 1587 (CFNetwork)
16:52:08 Resolved hostname (my-smtp-host.exchange).
16:52:08 Prepare secure connection...
16:52:08 Successful connection.
16:52:24 S: 
16:52:24 Error code: 8
16:52:24 New timeout values (8/8): 24/24
16:52:24 Failed action (0). Reset observed read/write timeouts: 8/8

16:52:24 Handling reply
16:52:24 Sending request (46)
16:52:24 Handling request
16:52:24 Clearing connection to my-smtp-host.exchange
16:52:25 Ready to run action (retry count: 1)
16:52:25 Clearing connection to my-smtp-host.exchange
16:52:25 Trying to connect to my-smtp-host.exchange on port 1587 (CFNetwork)
16:52:25 Resolved hostname (my-smtp-host.exchange).
16:52:25 Prepare secure connection...
16:52:25 Successful connection.
16:52:49 S: 
16:52:49 Error code: 8
16:52:49 New timeout values (8/8): 36/36
16:52:49 Failed action (0). Reset observed read/write timeouts: 8/8

And so on..

My server configuration (masked a bit) is:

SMTP Server: my-smtp-host.exchange
User Name: DOMAIN\me
Password:
Port: 1587
Require SSL: yes