IMAP Port 143 is not known as a secure connection (doesn't use SSL/TLS)... if I read right, it perhaps can use STARTTLS, but that is being obsoleted, it seems (see link below). IMAP Port 993 is used for secure connections only... I would guess that a server accepting connections on port 993 is going to force security to be used. It probably will -not- connect if you don't have SSL/TLS when you use port 993. But I'm just guessing, from reading the link below...
XN use 993 SSL.
http://xnotifier.tobwithu.com/dp/node/6
But the faq not specify that
But the faq not specify that use a secure connection also if the port 993 is usual.
Info
IMAP Port 143 is not known as a secure connection (doesn't use SSL/TLS)... if I read right, it perhaps can use STARTTLS, but that is being obsoleted, it seems (see link below).
IMAP Port 993 is used for secure connections only... I would guess that a server accepting connections on port 993 is going to force security to be used. It probably will -not- connect if you don't have SSL/TLS when you use port 993.
But I'm just guessing, from reading the link below...
Here's some interesting info from the Fastmail site...
https://www.fastmail.fm/help/technology_ssl_vs_tls_starttls.html