Some ISPs block out going SMTP email on port 25. It looks like Verizon is probably one of them:

https://kevinlawry.wordpress.com/2010/06/10/verizon-fios-blocking-smtp-port-outgoing-email/

You can probably fix it by changing the port that the iPad is using to send email, probably to port 465 or 857, which are typical ports supported when the ISP blocks port 25.
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