Hi Bryce,
If your mobile Wifi Router connects to an ISP, rather than your own infrastructure, you might find it is a security measure used by the ISP. Many "domestic" ISPs will block all SMTP access except for their own STMP Server. This limits the damage a Mailware/Virus Bot can do.
If so, just change your STMP to that recommended by the ISP (and you can probably turn off authentication) and it should work.
Regards
Bill