I misunderstood as well. OK let's try again. The WiFi really shouldn't matter in this case as long as you have a route from your device to the mail server in question. That may be Cellular, WiFi, Tethering. I personally don't have an email address with OneTel, I tried this with a Comcast and a Siteground-hosted domain and both worked - so it could very well be an issue with OneTel themselves. I did a little Google'ing and found that the incoming and outgoing mail server settings for OneTel are on different domains, which could be the issue. It looks like you use your email address as the username, but for the server settings:
Incoming = mail.onetel.com
Outgoing = smtp.onetel.net
At least they use standard ports (110 for POP, 143 for IMAP, 25 for SMTP).
If your email address is actually a onetel.net instead of a onetel.com then the settings are:
Incoming = pop.onetel.net
Outgoing = smtp.onetel.net
Again, standard ports so you shouldn't have to mess with those in any advanced settings subscreen.