Just ran into a case where it's obvious that Verizon is blocking IMAP from cellular devices (on their network) from reaching IMAP Servers on the Internet. eg: TCP/993 is being blocked. This was verified by asking the upstream to add a high numbered port as a work-around and then using the high numbered port for IMAP communications - worked without issue. There is absolutely no reason in this day and age to be blocking ports, especially ports intended for SSL/TLS based communication. This should be remediated as organizations will simply start offering services on other ports like TCP/443 to circumvent such things or users will gravitate to VPNs and Verizon won't even be able to discern what is flowing (removing all advertising opportunities).
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