This may seem a strange problem, but I am trying to connect to the Outgoing mail server, using Outlook. If I setup the IMAP configuration, and use my Verizon hot spot to connect to the internet, I can connect to the Outgoing mail server and send email. If I take the same laptop and plug it into my Cox router, though, I cannot connect to the Outgoing mail server. I have person at a different site, who has the same problem connecting to the same mail server, using Verizon DSL. He is not trying to connect by wireless. When I go onto the server and test the DNS and outbound route, everything tests fine. I cannot telenet to the mail server from the Cox connection. Is there something I need to do on site, or do I have to contact the various ISPs to get the connection to work?
Another possibility… some internet providers block outbound TCP/25 (SMTP) connections. I know mine does. I have to send (relay) outbound e-mail through their SMTP server. My internet provider also posted a knowledge base documenting how to configure your mail client to send outbound e-mail.
This may be a Verizon issue: “Verizon announced: “Maintaining the security and integrity of your information is important to us. Effective November 15, 2016, for enhanced security and phishing protection, we are eliminating the ability to use non-local “from” addresses in conjunction with your verizon.net email account.””