Port 25 is usually blocked by ISPs in their efforts to reduce spam.
If you use Apple mail via your ISP, you can see what port is in use the in the Apple Mail preferences. If you do not, your ISP should be able to tell you what port they recommend. They may have a support article online.
This article about using iCloud with TechTool Protection has some information about two-factor authentication:
Email alerts with iCloud two factor authentication
If none of this allows you to solve the problem, please send a message to
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, including a link to this thread, and mention your ISP. Thank you.