I use Mandrill for my outbound SMTP. For SSL, it operates through port 587.
I have had many occasions where my connection fails for no apparent reason. I'm just living my life and sending email and then, poof!, an email tells me it can't send with that server. I go through debugging and re-enter the credentials and it would work.
I started thinking "last time it happened, wasn't it the port number that was different then, too?" So, I changed the name of the server to "Mandrill, s/b port 587" so I would know.
It happened again today. I went to look at it the settings and there was a change to port 486. WTF?
I changed it back to 587 and it worked.
I have changed the setting "Automatically detect and maintain account settings" to be off. I'm going to be that stops the problem. If not, I'll update here. If it's been a long time since 5/15/15, you are safe in seeing that as a solution.